A composite casing for a coilable rule comprises a pair of inner, plastic case members and a thin, outer metal case which receives the plastic case members in a close fitting relationship. A center post is received in central openings provided in the plastic case members to support a measuring tape and coil spring of the rule. One end of the center post has an enlarged head and its other end receives an assembly screw extending through holes in the metal case to engage and hold the metal case in firm assembly with the plastic case members. A series of knurls is formed on the center post for engaging one of the plastic case members to hold the post firmly in place. Alternatively, the center post may be formed as an integral part of one of the plastic case members. A plurality of deformable ribs may be provided on the exterior surfaces of the plastic case members to engage the metal case and firmly hold the assembly together.

The present invention relates to a casing for a coilable rule and, more 
particularly, to an improved casing structure including a pair of inner 
plastic case members received in a thin outer metal case. 
U.S. Pat. Nos. 3,214,836 and 3,216,117, assigned to the assignee of the 
present invention, illustrate coilable rules of the type concerned in this 
invention. Generally, such rules include a coilable measuring tape and a 
coil spring contained within a protective metal casing. The casing 
typically consists of two separate die castings composed entirely of metal 
to provide a rugged structure which protects the rule against damage. The 
all-metal casing is relatively expensive to manufacture and results in a 
relatively heavy rule. In addition, frictional contact with the metal 
casing results in wear on the movable components of the rule, especially 
on the surface of the measuring tape at the location where it passes 
through the casing. 
An objective of the present invention is to provide an improved casing for 
a coilable rule which provides the same rugged structure and protective 
features of the all-metal casings previously used without the 
manufacturing expense associated with a solid metal casing. A primary 
purpose is to provide a composite casing consisting of a pair of inner 
plastic case members and an outer metal case which has the necessary 
toughness to withstand abuse and to remain securely assembled throughout 
the useful life of the casing. 
In addition, the invention is intended to provide an improved coilable rule 
casing which minimizes friction between the casing and movable components 
of the rule to reduce wear on the measuring tape. It is also intended to 
provide a coilable rule casing which is lighter in weight and easier to 
handle than conventional all-metal casings. 
The present invention achieves the above objectives in a casing for a 
coilable rule comprising a pair of inner, plastic case members each having 
a side wall provided with an inwardly extending, peripheral flange and 
adapted to fit together to provide a hollow chamber for receiving the 
measuring tape and coil spring, and a thin, outer metal case shaped to 
conform to the exterior configuration of the side walls and flanges of the 
inner plastic case members and adapted to receive the plastic case members 
in a close fitting relationship. Each plastic case member includes a 
central opening formed in its side wall. The metal case includes a pair of 
holes formed in its opposite sides in alignment with the openings in the 
plastic case members. A center post is received in the central openings in 
the plastic case members and extends across the hollow chamber for 
supporting the measuring tape and coil spring. One end of the post extends 
through one of the holes in the metal case and has an enlarged head for 
engaging the side of the metal case adjacent to the hole to hold the metal 
case against the adjacent plastic case member. The post includes a knurled 
surface for engaging one of the plastic case members in its central 
opening to hold the post firmly in place. The other end of the post has an 
inwardly extending axial bore to receive a screw provided with an enlarged 
headed end for engaging the opposite side of the metal case adjacent to 
the other hole to hold the metal case against the other plastic case 
member. 
Preferably, a series of knurls are formed on the center post adjacent to 
its enlarged head. The knurls provide firm engagement between the center 
post and one of the plastic case members to hold the metal case and 
plastic case member in a secure assembly. In addition, the knurls prevent 
rotation of the center post when the screw is threaded into its other end 
in the assembly of the rule. 
In a preferred embodiment of the invention, the outer metal case comprises 
a pair of mating case portions, each having a side wall and peripheral 
flange conforming in a close fitting relationship to the side wall and 
peripheral flange of the corresponding inner plastic case member. Further, 
in accordance with another feature of the invention, each plastic case 
member includes a plurality of deformable ribs provided on the exterior 
surfaces of its side wall and peripheral flange for engaging the interior 
of the metal case to securely hold the metal case and plastic case members 
together and to prevent relative movement therebetween. 
In an aternative embodiment of the invention, an integral, center post is 
formed on one of the plastic case members and extends across the hollow 
chamber into the opening provided in the other plastic case member. The 
post has an axial bore at its free end. A screw is threadably received in 
the axial bore and provided with an enlarged headed end for engaging the 
metal case to hold the metal case and plastic case members together. 
The invention achieves a casing for a coilable rule which is rugged in 
construction and light in weight. It also achieves a composite casing in 
which the inner plastic case members are held in firm assembly with the 
outer metal case. The use of plastic case members for the interior of the 
casing reduces the friction between the casing and movable components of 
the rule. As a result, the wear on the measuring tape is substantially 
reduced, particularly at the location where the tape passes through the 
casing. 
The improved casing of this invention substantially duplicates the 
configuration of the all-metal casing disclosed in U.S. Pat. No. 
3,216,117. Thus, with respect to more detailed structural features of the 
casing, reference should be made to the specification and drawings of U.S. 
Pat. No. 3,216,117, which is hereby incorporated by reference. 
The accompanying drawing illustrates preferred embodiments of the invention 
and, together with the description serves to explain the principles of the 
invention.

Referring to FIGS. 1 and 2, a coilable rule embodying the present invention 
comprises a casing, generally 10, which receives a coilable measuring tape 
12 and a coil spring 14 for winding the measuring tape into a coiled 
position within the casing. The rule also includes a pair of discs 15 
(FIG. 2) rotatably mounted on casing 10 at opposite sides of measuring 
tape 12 and coil spring 14. The pair of discs serves as a guide for 
measuring tape 12 and coil spring 14 to prevent frictional engagement 
between the casing and the edges of the measuring tape and coil spring. 
The structural details of the discs are described in U.S. Pat. No. 
3,216,117. 
Casing 10 is provided with a mouth (not shown) adjacent to its bottom wall 
through which measuring tape 12 passes when the tape is extended and 
retracted. The inner end of measuring tape 12 may be connected to the 
outer end of coil spring 14 by a tongue and slot connection (not shown) 
and the opposite end of the measuring tape is provided with a conventional 
hook 16 (FIG. 1). In addition, a locking mechanism, generally 18, may be 
provided, as disclosed and claimed in U.S. Pat. No. 3,214,836. 
The casing of the present invention includes a pair of inner, plastic case 
members or inserts 20 and 22 (FIG. 2) adapted to fit together to provide a 
hollow chamber for receiving measuring tape 12 and coil spring 14. 
Preferably, each inner plastic case member or insert consists of 
low-friction, high-impact plastic material, e.g., black ABS plastic. 
Plastic insert 20 includes a side wall 24 provided with an inwardly 
extending peripheral flange 26. A central opening 28, preferably circular, 
is provided in side wall 24 of plastic insert 20. A cylindrical boss 30 
extends inwardly from side wall 24 and surrounds circular opening 28. An 
inwardly tapered surface 32 is provided on the exterior of side wall 24 
around opening 28. 
Similarly, plastic insert 22 includes a side wall 34 provided with an 
inwardly extending, peripheral flange 36, a central spring 38, and a 
cylindrical boss 40 extending inwardly from side wall 34 and surrounding 
opening 38. As shown in FIG. 2, circular openings 28, 38 and cylindrical 
bosses 30, 40 are in axial alignment. Each disc 15 includes an annular hub 
portion 42 which receives the corresponding cylindrical boss 30, 40 of the 
plastic inserts. Plastic inserts 20 and 22 may be provided with a 
plurality of male-female connections 44 (one shown) which allow the 
inserts to fit together in a predetermined orientation to define the 
hollow chamber in which measuring tape 12 and coil spring 14 are received. 
Both inserts can be molded by known techniques. 
In accordance with the invention, casing 10 also includes a thin, outer 
metal case or skin shaped to conform to the exterior configuration of the 
side walls and flanges of the inner, plastic case members or inserts. 
Preferably, as shown in FIG. 2, the thin outer metal case comprises a pair 
of mating case portions 50 and 52 which receive plastic inserts 20 and 22 
in a close fitting relationship. Metal case portion 50 includes a side 
wall 54 shaped to conform to the exterior surface of side wall 24 of 
plastic insert 20 and a peripheral flange 56 shaped to conform to the 
exterior surface of flange 26 of the plastic insert. Similarly, metal case 
portion 52 includes a side wall 58 shaped to conform to the exterior 
surface of side wall 34 of plastic insert 22 and a peripheral flange 60 
shaped to conform to the exterior surface of flange 36 of the plastic 
insert. 
Metal case portion 50 includes an inwardly tapered, annular flange 62 which 
defines a circular hole in its side wall 54 in alignment with circular 
opening 38 of plastic insert 20. Similarly, metal case portion 52 includes 
an inwardly tapered, annular flange 64 which defines a circular hole in 
its side wall 58 in alignment with circular opening 38 of plastic insert 
22. As shown in FIG. 2, the hole defined by annular flange 62 is 
substantially larger than the hole defined by annular flange 64. 
Metal case portions 50 and 52 may be formed as a thin steel shell. 
Preferably, the thin steel is chrome plated to enhance its durability. 
A center post 70, preferably metal, is received in central openings 28 and 
38 provided in plastic inserts 20 and 22. Post 70 extends across the 
hollow chamber defined by the plastic inserts to provide a support for 
measuring tape 12 and coil spring 14. The inner end of coil spring 14 may 
be anchored to post 70. One end of post 70 extends through the large hole 
in side wall 54 of metal case portion 50 and has an enlarged head 72 for 
engaging annular flange 62 to hold the metal side wall against side wall 
24 of plastic insert 20. The other end of post 70 has an axial bore 74 
which, in the preferred embodiment, is internally threaded. This end is 
countersunk to provide an inwardly tapered, conical surface 76 for 
receiving annular flange 64 of metal case portion 52. 
In the preferred embodiment, as shown in FIG. 2, center post 70 includes a 
knurled surface 78 for engaging plastic insert 20 to hold the post firmly 
in place. Preferably, a series of knurls is formed around the exterior of 
post 70 adjacent to its enlarged head 72. With post 70 inserted in opening 
28, its knurled surface 78 engages plastic insert 20 along the inner 
cylindrical surface of boss 30 to hold the post firmly in place. The 
knurls secure post 70 to plastic insert 20 so that side wall 54 of metal 
case portion 50 is held against side wall 24 of plastic insert 20. The 
knurls also prevent undesired rotation of post 70 relative to plastic 
insert 20. 
An assembly screw 80 is received in threaded axial bore 74 in center post 
70. Assembly screw 80 is provided with an enlarged headed end 82 for 
engaging flange 64 of metal case portion 52 to hold its side wall 58 
against side wall 34 of plastic insert 22. 
In a preferred embodiment, a belt clip 90 may be mounted on the metal case. 
The belt clip comprises a generally flat, metal strip bent into the 
desired shape and provided with an inwardly tapered, annular flange 92 
which defines a circular hole for receiving assembly screw 80. Headed end 
82 of the assembly screw serves to fasten belt clip 90 to the metal case. 
Referring to FIGS. 3 and 4, in an alternative embodiment of the invention, 
an integral, center post 100 may be formed on plastic insert 20 in place 
of the separate post provided in the preferred embodiment of FIG. 2. The 
free end of post 100, which is received in central opening 38 of plastic 
insert 22, is identical in configuration to the corresponding end of post 
70 (FIG. 2). Accordingly, the same reference numerals are used to identify 
the structural features of post 100. 
Initially, the opposite end of post 100, which is integrally formed as part 
of insert 20, includes a cylindrical extension 102 which is received in 
the hole defined by annular flange 62 of side wall 54 of the metal case. 
As shown in FIG. 4, cylindrical extension 102 may be shaped into an 
integral retainer by conventional heating or ultrasonic techniques to lock 
annular flange 62 of the metal case to plastic insert 20. 
Preferably, in the alternative embodiment of FIGS. 3 and 4, post 100 may be 
provided with a hollow bore at its free end and assembly screw 82 may be a 
self-tapping screw. 
In accordance with another aspect of the invention, a plurality of 
deformable ribs may be provided on the exterior surfaces of the side wall 
and peripheral flange of each plastic insert for engaging the interior of 
the metal case to securely hold the metal case and plastic inserts 
together to prevent relative movement therebetween. As shown in FIG. 5, 
which is a greatly enlarged view, a plurality of deformable ribs 104 may 
be provided on peripheral flange 36 of plastic insert 22. When metal case 
portion 52 is assembled over plastic insert 22, ribs 104 on peripheral 
flange 36 are deformed as the ribs move into contact with peripheral 
flange 60 of the metal case. The deformed ribs enhance the frictional 
engagement between the plastic insert and metal case portion to securely 
hold these components together. Similar deformable ribs may be provided on 
all exterior surfaces of plastic inserts 20 and 22. 
The present invention is not limited to the specific details shown and 
described, and modifications may be made to the coilable rule casing 
without departing from the principles of the invention.