Test tube holder insert

A unitary test tube holder insert adapted for receiving test tubes. The insert has a first ring to be secured in a hole of a test tube rack. A plurality of spring members extend at one end from the first ring towards a center axis of the ring to resiliently engage the outside of a test tube inserted into the insert. The spring members are connected at their other end to a second ring which is arranged coaxially with the first ring along the center access, and each spring member is curved towards the center axis to exhibit a straight section which extends parallel to the center axis and which resiliently engages the outside of a test tube inserted into the insert.

TECHNICAL FIELD 
The present invention relates to a test tube holder insert to be inserted 
into a hole in a test tube rack for receiving test tubes of different 
diameters, comprising a ring to be secured in said hole and being provided 
with spring members extending from the ring towards the centre axis of the 
ring to resiliently engage the outside of a test tube inserted into the 
insert. 
BACKGROUND OF THE INVENTION 
Such test tube holder inserts are known. A cross-sectional view of such a 
known test tube holder insert is shown in FIG. 1 on the appended drawing. 
The insert shown comprises a ring 1 which in a manner not shown in any 
greater detail, is designed to be snapped in place in any of the holes in 
a tray provided with holes for receiving test tubes and belonging to a not 
shown test tube rack. In the embodiment shown, the ring 1 is provided with 
spring members in the form of resilient tongues 2, which extend obliquely 
towards the centre axis of the ring 1. 
It has, however, been found that an insert designed in this manner, does 
not ensure that the test tubes in fact stand vertically in the test tube 
rack. This is particularly important in order to avoid spillage in 
connection with e.g. automatic pipetting of radioactive or other toxic 
liquids in certain applications. 
Test tube racks having two trays provided with holes and arranged above 
each other with the holes aligned for receiving test tubes, are also 
known. In such test tube racks, inserts of the kind shown in FIG. 1, are 
secured in the holes in both trays. Hereby, a more stable but not 
completely reliable fixation is obtained of the lower portion of the test 
tubes since, after all, the test tubes can end askew. 
BRIEF DESCRIPTION OF THE INVENTION 
The object of the invention is to bring about a test holder insert for test 
tube racks, which insert, for test tubes within a certain range of 
diameters, ensures the vertical alignment of the test tube in test tube 
racks having one as well as two trays provided with holes. 
This is attained by means of the test tube holder insert according to the 
present invention in that the spring members are connected at their other 
end to a second ring which is arranged coaxially with the first-mentioned 
ring along its centre axis, and that each spring member is curved towards 
said centre axis to exhibit a section which extends parallel to the centre 
axis and which resiliently engages the outside of a test tube inserted 
into the insert.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 2 is a perspective view of an embodiment of a test tube holder insert 
according to the invention. 
The test tube holder insert shown in FIG. 2, is intended to be secured in a 
hole in a test tube rack in order to make it possible to receive test 
tubes of different diameters therein. 
FIG. 3 is a schematical sectional view of an embodiment of a test tube 
rack, known per se, with two trays 3 and 4 provided with holes for inserts 
according to FIG. 2, and arranged above each other. The test tube rack 
shown also comprises an underlying tray 5 which is adapted to support, 
from below, test tubes placed in the test tube rack. Two test tubes, 
denoted 6 and 7, respectively, of different diameters have been inserted 
into the inserts as shown in FIG. 3. 
The test tube holder insert according to the invention, shown in FIG. 2, 
comprises a ring 8 as the known insert shown in FIG. 1. On its outside, 
that ring is provided, on the one hand, with a number of hook-shaped 
elements 9 and, on the other hand, with a number of protrusions 10, which 
are adapted to co-operate in order to secure the insert according to FIG. 
2 in the test tube rack according to FIG. 3 in such a manner that the 
underside of the protrusions 10 will engage the upside of the tray 3, 
while the hook-shaped elements 9 will snap in against the underside of the 
tray 3 as clearly apparent from FIG. 3. The hook-shaped elements 9 are 
designed resilient so that they spring away when they are brought through 
the hole in the tray 3 to thereafter snap in against the underside of the 
tray 3. 
Of course, the ring 8 can be uniform around all of its circumference but 
the design shown in FIG. 2 with the radially projecting protrusions 10, is 
preferable from a manufacturing point of view. 
The test tube holder insert according to the invention also comprises a 
ring 11 which is arranged coaxially with the ring 8 along its centre axis. 
According to the invention, a number of spring members 12 extend between 
the rings 8 and 11. The number of spring members 12 is four in the 
embodiment of the test tube holder insert according to the invention, 
shown in FIG. 2. Of course, the number of spring members 12 can be greater 
than four but has to be at least two in order for the insert according to 
the invention to function in a desired manner. 
According to the invention, the spring members 12 are curved towards the 
centre axis of the rings 8 and 11 to individually exhibit a section 13 
which extends along the centre axis at a predetermined distance therefrom. 
The surfaces of the sections 13 of the spring members 12, facing the 
centre axis, are intended to resiliently engage the outside of a test tube 
inserted into the insert such as the test tubes 6 and 7 shown in FIG. 3. 
The length of the sections 13 is e.g. around 5 mm for inserts having a 
length of around 32 mm. 
In the embodiment shown in FIG. 3, the sections 13 of the spring members 12 
are concealed by the respective test tube 6 and 7. 
On a comparison of the two inserts with the test tubes 6 and 7, 
respectively, of different diameters, the insert is prolonged downwards 
the greater the diameter of the test tube is, as apparent from FIG. 3. 
In order to further ensure the vertical alignment of the test tubes in the 
test tube rack according to FIG. 3, the insert according to the invention 
is provided with guiding elements 14. These guiding elements 14 are 
intended to guide the prolongation movement of the lower portion of the 
insert in a vertical direction in the hole in the tray 4 when a test tube 
is inserted into the insert and, at the same time, restrict the horizontal 
movement of the lower portion of the insert in that hole. 
In the embodiment of the test tube holder insert according to the 
invention, shown in FIG. 2, the guiding elements 14 comprise guiding pins 
projecting from the ring 11 towards the ring 8. These guiding pins extend 
parallel to the centre axis of the rings 8 and 11 and are adapted to 
engage, with their outsides, the hole wall of a hole in the tray 4 in the 
test tube rack shown in FIG. 3 for test tubes of all diameters that could 
come into question for the insert. 
According to a preferred embodiment of the test tube holder insert 
according to the invention, the spring members 12 are articulately 
connected to the rings 8 and 11. This is accomplished in that notches 15 
are formed in the outside of the spring members 12 at the transition 
between the spring members and the rings 8 and 11, respectively. Of 
course, the notches 15 are not necessary but are preferable in certain 
applications where some kind of a hinge function is required between the 
rings 8 and 11, and the spring members 12, e.g. to avoid that the pressure 
from the spring members 12 will be too great on test tubes of larger 
diameters within the range of diameters in question. 
The test tube holder insert according to the invention is made of plastic, 
e.g. polyetheretherketone, and injection moulded in one piece. The test 
tube holder inserts according to the invention are manufactured to be able 
to receive test tubes whose diameters lie within certain intervals such as 
5-12 mm, 10-16 mm and 15-24 mm. Due to the design of the spring members, 
the test tube holder insert according to the invention will be very stable 
and will guarantee a vertical alignment of the test tubes within the 
interval of diameters in question in the test tube racks of today.