Split head hammers

A split head hammer including a head (4) from one end of which a replaceable hammer shaft (2) projects, comprising two head parts (4A, 4B) which can be connected to grip a pair of striking pieces (11) and the shaft (2), the shaft being sunk fully within the head. The head grips the shaft at a plurality of circumferentially-shaped positions (70). Striking pieces suitable also for use in other designs of hammer e.g. solid head and having a rearward extension (46) of smaller section than the open end (21) of the socket can be retained in the socket by plastic flow and/or by a separate retainer, preferably an annular metal washer (50, 60) usefully toroidal (60). Not only the striking pieces (11) but also the shaft (2) can be simply replaced by the user, notwithstanding that the hammer is suited to heavy-duty use.

This invention relates to split head hammers, and in particular to split 
head hammers with a rigid e.g. metal or plastic head carrying at one but 
usually at each end a replaceable striking piece. 
In a split head hammer, a striking piece is replaced when worn or as 
required for different hammer applications by separating or "splitting" 
the head, usually into two main parts. When assembled or re-assembled the 
parts form a socket or sockets in which the striking piece(s) is/are 
retained. 
The striking piece is conventionally a cylindrical slug of rawhide such as 
water buffalo rawhide but for applications requiring a striking piece of a 
different hardness it can be of another firm but malleable material such 
as leather, rubber, hardwood, a synthetic resinous material and some 
metals such as copper and aluminium. Often the two striking pieces in a 
split head hammer are of different materials. 
In common with other hammer designs, it is essential in split head hammers 
that each striking piece is properly gripped in the hammer head, and that 
the hammer head in turn is safely secured on the hammer shaft, in both 
cases so that there cannot be unexpected and perhaps dangerous 
disengagement during use. 
One known design of split head hammer in current widespread use for heavy 
duty applications follows the teaching of Colvin U.S. Pat. No. 562581 
(FIG. 3); in the production embodiment the sockets are however of 
frusto-conical form in that they each comprise a base and sides tapering 
radially inwardly towards a socket open-end. Each striking piece is 
respectively positioned to abut the base, which absorbs the hammer 
impacts, the striking piece being trapped and gripped in the socket by the 
inwardly tapering socket sides. This retaining arrangement has proved 
suitable for the softer striking pieces, such as rawhide, since the 
available closing movement of the parts provides a grip adequate to 
prevent the striking piece flying free from the head, under the 
centrifugal forces generated during use, without the need for ridges, 
spikes or other costly and complicated projections on the inner surface of 
the socket, whilst allowing the major portion of the striking piece to 
project from the socket open end for extra working volume. 
A disadvantage of this first known design is that the hammer shaft cannot 
simply be replaced by the user. Another disadvantage is that the head 
parts are necessarily dissimilar in shape and so expensive to make and to 
store. A third disadvantage is that this known hammer is complicated to 
assemble. A fourth disadvantage is that there can be considerable wastage 
of time and material if during initial assembly the wedges being driven 
into the shaft end to locate the hammer head safely on the shaft cause the 
shaft to fracture. Briefly, in this known construction, one head part is 
of generally T-form with a top section comprising two part-sockets and a 
hollow shaft-receiving stem, and the other part is of part-cylindrical 
form comprising two matching part-sockets and a central aperture sized to 
receive the stem. The hollow stem is externally threaded to receive a nut 
used to tighten the head parts around the striking pieces. During initial 
assembly, the nut is fed over the shaft head end, followed by the two head 
parts (the said other part followed by the said one part), whereafter the 
shaft head end is "permanently" expanded outwardly against the hollow stem 
by wedges driven axially into its head end. The shaft is further secured 
to the one part of T-form by a pin driven through aligned holes in the 
hollow stem and so through the shaft, with the exposed pin ends then being 
flattened against the outer surface of the hollow stem. 
We have recognised that a desirable feature of this known design is that 
the shaft is fully sunk between the sockets and so is able to receive 
directly the impacts from the striking pieces, over a long supported 
length; and it is one object of our invention to provide a split head 
hammer which includes a shaft together with a head defining a socket or 
sockets, in which the shaft extends behind a socket or between the 
sockets, but yet in which the shaft is removably secured to the head. 
Thus according to one feature of our invention we provide a split head 
hammer including a head and a shaft, the head comprising a first part and 
a second part, the parts being connected to form at least one striking 
piece socket, the head including a hollow stem having an open end, the 
shaft having a portion axially located in and substantially filling the 
hollow stem and projecting from the open end, the stem extending behind 
the socket so that impacts taken by the socket from the striking piece are 
transmitted directly to the shaft characterised in that the stem is formed 
when the parts are connected together, and in that the stem has a closed 
end, the closed end having a larger cross section than the open end, and 
in that the shaft portion has a region which is of larger cross-section 
than that of the open end. In a preferred construction, the closed end is 
formed by a pair of end members integral respectively with each head part, 
and spaced apart by a narrow gap through which the shaft cannot pass i.e. 
the shaft portion has no cross-section smaller than this gap. Axial 
slippage of the head along the shaft in one relative direction can thus be 
prevented by abutment of the shaft head end with the closed end of the 
socket, the closed end preferably being flat for full facial contact with 
the end face of the shaft head end, or conical for annular contact over a 
substantial area of the end face; whilst slippage of the head on the shaft 
in the other relative direction under centrifugal force during swinging of 
the hammer in use can be prevented by engagement between the shaft 
cross-section and the stem cross-section, preferably by the wedging action 
of a steadily increasing shaft cross-section with a corresponding steadily 
reducing stem cross-section. With properly selected dimensions, the shaft 
cannot be removed through the open end of the stem whilst the head parts 
are connected. 
Because the stem is formed by the joining of the head parts, the shaft can 
be replaced after the head has been split, and is retained when the parts 
are re-connected. The closed end can also be split, into two sections with 
one section integral with each head part. This embodiment permits the 
shaft to be placed in one head part, then the other head part can be 
secured both to trap the shaft, and to form the sockets and to trap the 
striking pieces therein, the split being parallel to the shaft axis; 
furthermore whilst this embodiment greatly eases hammer assembly as 
compared to the existing prior arrangement described above, we do not 
exclude, in an alternative embodiment particularly useful for the larger 
split-head hammers having a handle portion of smaller section than the 
head end, an arrangement wherein the closed end is provided by a 
non-integral cap positioned and secured after the shaft has been fed 
axially through a hollow stem (which is internally frusto-conical to match 
the respective part of the shaft contour with which it is to mate, and 
with the diminishing section towards the open end). 
If required, the internal surface of the stem can be provided with one or 
more projections which upon initial assembly of the head parts indent the 
shaft, and which permit accurate angular and axial re-alignment of a 
replaced (e.g. elliptical or oval) shaft in the stem upon subsequent 
re-assembly e.g. after replacing a worn socket piece. 
Another widely-used design of split head hammer, usually for lower duty 
applications, follows the teaching of German GM8416694 and GM8416695. It 
includes a head formed of two parts split parallel to the shaft axis, the 
parts being connected by a single nut and bolt assembly located on the 
stem axis; this assembly is tightened until the sockets grip the striking 
pieces, but the gripping force has to be transmitted from the stem axis to 
the sockets, and to help ensure a grip sufficient to prevent the striking 
pieces from flying free under centrifugal force, the sockets are of an 
extended length (so reducing the volume of the striking piece available 
for useful work, whilst increasing the weight of socket material used), 
and internally ridged. We seek to avoid these disadvantages. Thus we 
connect the parts between the stem and each socket, the connection 
preferably being by a pair of nut and bolt assemblies positioned along the 
axis of the sockets, with one to either side of the stem; though in an 
alternative but less preferred embodiment we could use screws with tapped 
recesses. Usefully the parts will have aligned bolt receiving apertures, 
each terminating in a hexagonal recess, so that one recess can locate a 
nut whilst the other can receive a cap screw; an advantage of this 
arrangement, apart from the angular location of the nut during assembly 
and dis-assembly, is that each recess can be outside the axial projected 
area of the stem so that a strong beam section can be provided between a 
socket and the stem to help resist the input loads from the striking 
piece--the bolt-receiving apertures are provided in this beam section 
which also helps define the aforementioned socket base. We have found it 
desirable to shape the socket base to a deepening conical form, so that 
the beam section is initially of substantially constant depth (parallel to 
a socket axis) inwardly from the closed end of the stem and then deepening 
towards the open end of the stem, which is an advantageous design since 
many (mis-directed) hammer impacts are taken by the inward edge of a 
striking piece rather than "full face". Furthermore, the sockets are 
shaped to a frusto-conical form reducing in diameter to their open-end, to 
assist retention e.g. of a striking piece which we have designed to have a 
portion of reduced section and which spreads within the socket, after 
fitting in the socket, when compressed by impacts at its striking end, 
and/or which can be mechanically coupled to a socket and within the socket 
by a separate retaining member, conveniently annular. 
The base and part of the socket surface are defined by the beam section, 
the beam section perpendicular to the stem axis having a greater depth 
along the axis of the sockets than has the stem wall in a direction at 90 
degrees thereto; whilst the dimension at 45 degrees thereto is greater 
still. Providing the extra material only where it is needed permits we 
believe the head to have a greater capacity to absorb vibrations from the 
striking pieces to help cushion the shaft from these vibrations, and 
protect the user's hand. 
Part of the beam section is outwardly extended; thus the head section 
between the stem and socket has a pair of outward extensions each parallel 
to the shaft axis, the connection between the said parts being by a 
threaded assembly comprising a nut and bolt, at least one of each nut and 
bolt being located in a recess in a respective outward extension. 
Preferably most or all of the recess is outside the tangent perpendicular 
to the major axis of the stem. The extension is less deep than the beam 
section. 
Because our improved hammer design makes it suitable for heavy duty 
applications, it is particularly necessary to consider operator muscular 
reaction to the vibrations resulting from the hammer impact loads; these 
should both be kept to a minimum and so far as possible prevented from 
reaching the user's hands and arm, where they can cause discomfort, 
fatigue and perhaps muscular stress and injury. We thus provide shaft 
damping means in the form of a collar-like extension to the stem. It will 
be understood that by locating the stem behind the socket or between the 
sockets, the shaft in our invention is already supported over a longer 
length than for the known low duty hammer (as compared to one existing 
hammer with an extra 50% of supported length) so reducing the amplitude of 
the vibrations by a reduced input unit loading to the shaft. With our 
proposed stem extension, the enclosed length of shaft can be further 
increased. The stem thus includes a first portion aligned with the socket 
and a second portion extending therefrom, the second portion being at 
least one quarter and preferably between one third and one half of the 
length of the first portion. Preferably the second portion comprises a 
pair of part-cylindrical extension members each mounted respectively on a 
head part in cantilever so that they can act when necessary as individual 
damping members; i.e. the collar-like extension is spaced from the nut and 
bolt assemblies. 
With wooden shafts in particular, despite the recognised need in the 
assembled hammer for the shaft to be tightly gripped, we have realised 
that care must be taken during assembly not to apply clamping loads (from 
the tightening of the head parts) of a magnitude sufficient to separate or 
force apart a significant proportion of the shaft fibres, so causing a 
substantial reduction in the shaft tensile strength. We have an improved 
stem to shaft geometry which can ensure a reliable grip on the shaft, by 
using dissimilar mating cross-sections. Thus according to a further 
feature of our invention we provide a split head hammer including a head 
comprising a first part and a second part, the parts being connected to 
form at least one striking piece socket and a hollow shaft-receiving stem, 
the connection between the parts being tightenable to reduce 
simultaneously the cross-section of the socket and of the stem 
respectively to grip firmly the striking piece and the shaft, the stem 
having an internal surface which engages the shaft at a plurality of 
circumferentially spaced positions, characterised in that during 
tightening the stem internal surface engages between one third and three 
quarters of a shaft circumference. Preferably for a wooden shaft, the stem 
engages 60-68% of a shaft circumference, for a high density polyethylene 
shaft 75%, and for a fibreglass shaft 60-65%; though for shafts e.g. of 
selected synthetic resinous materials, the stem may prior to head 
tightening engage as little as 10% of a shaft circumference, the minimum 
engagement area in each case being determined by the need to avoid 
stressing the material of the shaft beyond its elastic limit when the head 
parts are tightened so that the shaft can recover to or towards its 
initial size and shape upon subsequent release of the head parts i.e. so 
that the shaft (as well as the striking pieces) is again gripped tightly 
when one or both striking pieces are replaced and the head parts 
re-tightened. As a particular feature, to assist in correctly re-locating 
a shaft, the head parts can include bosses, preferably frusto-conical, 
which locate in indentations in the shaft, and whilst conveniently the 
indentations will have been formed during initial hammer assembly in the 
factory, replacement handles can be supplied ready-indented; the bosses 
can also help retain the handle in the hammer head. 
For a conventionally-sized shaft with the usual elliptical cross section, 
we prefer the stem internal surface to comprise two part-circles, each 
with its centre to the respective far side of the stem axis; this 
arrangement provides four circumferentially spaced stem to shaft 
engagement positions, occupying about 65% of each respective shaft 
circumference and leaving 35% of the shaft circumference initially spaced 
from the stem internal surface. After tightening of the nut and bolt 
assemblies, with the resultant compressive forces being applied at the 
four symmetrically spaced positions, the shaft is compressed to reduce its 
contact diameter by about 2 mm, shaft material then undergoing we believe 
plastic flow into the spaces between the four compression locations. We 
have found that without these plastic flow areas, the compressive loading 
required to force a 2 mm contraction on shaft diameter cannot be accepted 
even by the high tensile bolt and nut assemblies we employ. But without 
such reduction in shaft diameter, at least at selected locations around 
the shaft circumference, adequate gripping of the striking pieces cannot 
be guaranteed, and this is a particular problem if the length of striking 
piece sunk within a socket is to be reduced (to limit the waste of 
striking piece material). We have found we can reduce the diameter of a 
wood shaft 10-15% without it being significantly weakened, using a 
mechanical interlock from dissimilar cross-sections, but without 
impalement; we have suggested that too high a mechanical compression will 
cause the fibres of the shaft to separate and perhaps split, with serious 
weakening of the shaft, and for certain woods we thus keep the compression 
below 10% when necessary, as easily determined by simple experiments and 
achieved by varying the percentage amount of the contact area. 
For striking pieces such as those of malleable copper or aluminium, we 
believe it is desirable to provide an alternative gripping means to those 
currently available, to limit the length of striking piece needed simply 
for retention and thus also the depth of the sockets. In some current 
production designs a larger length socket has been provided when such 
striking pieces are to be used, but this results in a larger unused volume 
of material. Thus according to yet another feature of our invention we 
provide a hammer including a head comprising at least one striking piece 
socket, the socket having an open end to receive at least part of a 
malleable striking piece, and retaining means for the striking piece 
located between and engaged with said part and with the socket 
characterised in that the retaining means is positioned to sustain impact 
loading from the striking piece, the retaining means being adapted more 
firmly to retain the said part in the socket upon said impact loading. 
Preferably the said part is a rearward extension which is retained in the 
socket by an annular deformable ring. The annular ring can be of a 
cross-section to deform radially outwards along the socket base under 
axial impact loads, to behind the conventional socket retaining section; 
and in one embodiment the rearward extension is a column with a central 
recess and a splayed base-engaging end. In a preferred embodiment, an 
annular spring steel washer is located in the socket with its outer 
periphery at the junction between the base and the socket frusto-conical 
retaining wall, and its inner periphery against the cylindrical column, 
the washer penetrating the column and/or the column spreading around the 
washer upon a suitable loading of the striking piece e.g. an operational 
impact loading. 
Preferably we use a toroidal mild steel ring around the cylindrical column. 
The column is inserted in the socket with its splayed end engaging the 
socket base, and with the ring located at the junction between the base 
and the socket retaining section, whereupon the sub-assembly is forced 
further into the socket, as by impact loading, until e.g. the splayed end 
spreads along the base behind the ring. The toroidal shape of the ring 
backs up the insert face of the striking piece so as to inhibit too great 
a volume of the striking piece flowing into the socket cavity. Thus the 
striking piece material is forced to change its shape with plastic 
deformation to allow firm retention in the socket, with economy of 
material; and yet can be easily removed (and replaced) upon the head parts 
being separated.

The split head hammer includes an elliptical cross-section shaft 2 and a 
head 4. Hammer head 4 is assembled from identical parts 4A, 4B, secured 
together by nut and bolt assemblies 5. As best seen in FIG. 3, head 4 has 
a hollow receiving stem 6 effectively closed at one end by cover 8 formed 
by a pair of end members 8A (FIG. 7) respectively integral with parts 4a, 
4b and spaced apart by gap 26 (FIG. 2); though in an alternative 
embodiment this one end of the stem can be fully closed by a separate end 
plate (not shown) secured to one or both head parts. The stem 6 is open at 
the other end to receive the shaft 2, the shaft 2 in use projecting out of 
this other end 18. Head 4 also has aligned, opposed sockets 10 (FIG. 3) to 
receive cylindrical striking pieces 11 e.g. of rolled rawhide. Stem 6 
extends between sockets 10, and between nut and bolt assemblies 5 which 
are located to connect parts 4a, 4b between stem 6 and sockets 10, with 
assemblies 5 intersecting axis 15 of sockets 10. 
The shaft 2 is typically of length 295 mm, and reduces in section from its 
head end 3 with a 2.4 degree taper for 83 mm, so that the major axis of 
the elliptical shaft 2 reduces from 32.5 mm to 27 mm, and the minor axis 
from 28 mm to 22.75 mm. Stem 6 is sunk 43 mm into head 4, which also 
includes an annular extension 12 for stem 6, the extension 12 being 
mounted in cantilever on head 4 at a position spaced from nut and bolt 
assemblies 5, and terminating 63 mm from the head end 3 to provide (when 
head parts 4A, 4B are assembled) a long supported shaft head length; the 
separate extensions 12 can add an anti-vibration or damping characteristic 
to shaft 2. The stem 6 has a frusto-conical internal surface 20 also with 
a taper of 2.4 degrees, the shaft 2 having a major diameter at the 
extension end of 28 mm and a minor diameter of 23.5 mm. Stem 6 can have 
locating projections 27 (FIGS. 5/5A) to help the user re-align shaft 2 
during re-assembly, and which preferably are in the form of a pair of 
upstanding conical protrusions 27C (FIG. 5A) i.e. projecting inwardly of 
the hollow stem 6; though alternatively the projections 27 are ramps with 
faces 27A more steeply angled than faces 27B to bias the shaft with a 
wedging action towards the closed end of the hammer head. 
The foot 14 of the shaft 2 has a major axis of 39 mm and a minor axis of 
34.5 mm, whereas the hand-gripping area 16 has a major axis of 32 mm and a 
minor axis of 27.5 mm, which dimensions have been found suitable to permit 
a comfortable yet firm hand grip. 
Each socket 10 includes a deepening conical base 17 and a frusto-conical 
wall 19 forming a retaining section for the received striking piece 11, 
and reducing in diameter towards the socket open end 21, which 
conveniently has a diameter of 36.75 mm. 
It is a feature of our arrangement that the head parts 4A and 4B are 
identical, so simplifying manufacture, inventory control and replacement 
servicing. In use, the identical parts 4A, 4B are connected securely but 
releasably together by the nut and bolt assemblies 5, which pass through 
apertures 22 (FIG. 4), the nuts and cap screw heads being located in 
hexagonal recesses 24. When the striking pieces are trapped in sockets 10 
formed by the parts 4A, 4B, these parts are out of contact, being 
separated by gap 26 of a size to ensure that the striking pieces are 
firmly gripped no matter how deformable or malleable the material of which 
they are made. Release of assemblies 5 allows one or both striking pieces 
to be replaced, or the shaft 2 to be replaced. 
As can be seen from FIG. 4, apertures 22 are outside the tangent to the 
major axis of stem 6, as is most of recess 24. As can be deduced and seen 
from FIGS. 1 and 3 respectively, apertures 22, and recess 24 into which 
they lead, and thus the nut and bolt assemblies 5 are on the centre line 
15 of sockets 10. As can also be seen from FIG. 3, apertures 22 are in the 
beam section 25 defining the base 17 of socket 10, and part of the 
internal surface 20 of stem 6, the beam 25 thus being between the socket 
10 and the stem 6. As seen in FIG. 4, the recesses 24 are outside the 
axially projected area of the stem 6. The beam sections 25 are of greater 
width W1 than the head section W2 therebetween in which is the stem 6. As 
seen in FIG. 5, because base 17 is conical beam section part 25A is of 
generally constant depth, whereas beam section part 25B increases in depth 
towards the open end 18 of stem 6 and extension 12. i.e. the beam section 
25 has a greater depth in the direction of socket 10, adjacent open end 18 
than adjacent closed end 8. 
The striking piece 40A can have a cylindrical projection or column 46 (FIG. 
8) with a central recess 48. This design is particularly suitable for a 
striking piece of a less malleable material such as copper or aluminium, 
particularly when used in conjunction with a tapered annular washer 50 
located at its outer periphery at the junction between base 17 and wall 19 
and at its inner periphery around column 46; when the surface 44 is 
impacted, the washer imbeds in the column 46 and/or the material of the 
column flows around the inner periphery of the trapped washer. 
A particularly valuable embodiment is that of FIGS. 9-11, in which a 
toroidal mild steel ring 60 is positioned around column 46 of striking 
piece 40B is a sub-assembly (FIG. 9) prior to positioning in socket 10 
(FIG. 10); substantially only column 46 is positioned in the socket 10. 
Following impacting into socket 10 (FIG. 11) the material of the striking 
piece 40B has been plastically deformed and so forced to change its shape, 
the deformation being controlled and exploited in that the ring 60 also 
has its configuration changed until it is securely retained both in the 
socket 10 and around the column 46 and behind the rear face 62 of the 
striking piece (the rear face 62 itself deforming with plastic flow along 
and around the ring 60, whilst the outer perimeter 62A may undergo plastic 
flow about the perimeter of the socket open end). The deformed retaining 
ring prevents too great a proportion of rear face 62 plastically deforming 
into socket 10, to avoid too great a reduction in the volume of striking 
piece 40B available for useful work. Thus we secure improved retention, 
yet with reduced wastage or loss of effective volume of striking piece 
material. 
The split head hammer of our invention can thus be multi-use, since sockets 
10 can accommodate a variety of striking piece materials, which can be 
readily changed when required for different applications, or exchanged 
when worn. 
It will be understood that the above designs of striking piece are intended 
to permit a minimum length of striking piece to be used simply for 
retention in the head, which is a particularly valuable feature when the 
cost of e.g. copper is so high, and when therefor as great a proportion as 
possible of the striking piece must be available for useful work. 
As seen in FIG. 12, the shaft 2 is of wood and is of elliptical 
cross-section and is engaged by stem 6 at four angularly-spaced positions 
70, which together initially engage 65% of the shaft circumference. When 
the head parts 4A, 4B are fully drawn together to grip the striking pieces 
11, the material of shaft 2 extrudes or flows with plastic or equivalent 
deformation into the intervening spaces 74, initially representing 35% of 
the shaft 2 circumference. The internal surfaces 76 of head parts 4A, 4B 
are part-circular, each having a radius R about respective displaced 
centre 78A, 78B. The geometry of displaced part-circular head parts and an 
elliptical shaft permits a high compression loading to be applied to the 
shaft, sufficient not only for the shaft to be properly gripped with a 
controlled maximum loading so that it is not weakened by internal rupture, 
but also with the required loading being applied to the striking pieces, 
perhaps with a set loading to the striking pieces, and a varied loading to 
the shaft (in accordance with the dimensions, tolerances, durability etc. 
of the different striking pieces used) accompanied by plastic flow into 
spaces 74. 
In FIG. 5A, a pair of frusto-conical locators 27 are shown, which in use 
are in an intervening space 74. The locators 27C are in the form of bosses 
which engage in indentations in the shaft to help locate the shaft axially 
and angularly e.g. when the head parts 4A, 4B are being re-connected after 
replacement of a striking piece. In an alternative embodiment to that of 
FIG. 5, the locators 27 will extend axially, and also will be positioned 
in the intervening spaces 74 (FIG. 12), and so not contributing to or not 
substantially contributing to the axial location of the shaft 2 in head 4. 
The striking piece arrangement of FIG. 8 is particularly useful in split 
head hammers, since the heads 4A, 4B, can be released to ease removal of 
the inbedded washer 50. However, we forsee that this embodiment could also 
be used with a conical socket 10 i.e. since the frusto-conical retaining 
walls 19 of the FIG. 8 embodiment are not essential to a firm retention of 
the striking piece 40A in the socket, this arrangement using an annular 
washer can be used with a variety of socket designs. Specifically, we 
foresee a considerable usage with solid head hammers (i.e. non-split) 
where it is already the practice to "chisel out" the worn striking piece, 
so that in our proposal the striking piece would be positioned in the 
solid head with the reduced section mechanically coupled to the socket by 
a separate retaining member such as the disclosed annular rings or e.g. 
radial fingers. The striking piece 40A and washer 50 could for the solid 
head and split head hammers if required be provided as a sub-assembly (as 
anticipated in FIG. 8) or separately. It will also be understood that the 
problem of removing striking pieces from existing socket designs, many of 
which require the socket to be swaged onto the striking piece and/or for 
the side wall 19 to have upstanding projections for striking piece 
retention, is often accentuated by the tight initial engagement needed to 
allow for any subsequent relaxation or spreading of the side walls 19. It 
is thus an advantage of our embodiment of FIGS. 9-11 that outer perimeter 
62A flows around the socket end to inhibit outward spreading of the open 
end of the socket. 
The annular ring 60 of the FIG. 9-11 embodiment is selected by simple 
experiment to have small resistance to curling i.e. towards and away from 
its axis (FIG. 10 to FIG. 11), but a high resistance to axial compression 
to provide a barrier against inward flow of striking piece material under 
usage impacts. The length of the column 46 can thus be reduced, with a 
further saving of the volume of material used for retention of striking 
piece 40B. As with the embodiment of FIG. 8, the striking piece 40B is 
self-locking in the socket, upon initial impact(s) at surface 44.