the support 16 are downwardly extending elongated fingers 17 which terminate in enlarged heads 18 each enlarged head 18 has a conical end 19 and flat shoulder 20 as can be seen in the right hand side of fig2 which is partial sectional view along the line aa of fig3 the finger 17 is relatively thin and terminates in the shoulder 20 this shoulder is the back side of the external head 18 as can be seen the shoulder 20 extends outwardly from the exterior portion of the finger 17 the fingers 17 are arcuate sections separated by spaces 26 thus providing necessary resilience to the fingers 17 when this set of fingers 17 is pushed down through the hole 13 each finger is moved radially by the conical surface 19 towards the axis of the hole so that each head 18 passes through the hole 13 the resilience of the finger 17 snaps the head outwardly and the shoulder 20 engages the backside of tray element 12 the arrangement of the fingers 17 and their enlarged heads 18 and shoulders 20 firmly secures the support 16 with respect to the tray 12 so that it is essentially impossible to accidentally remove support 16 from the tray despite rough handling dropping etc in a preferred form of the invention the clamping member 14 is made of a resilient sterilizable material such as a synthetic rubber as is well known in the medical art the support element 16 is preferably molded from high impact strength semi rigid medical grade polymeric material or the like preferably the two sets of four fingers 17 are integrally molded into the support elements 16 as shown in fig4 a 4b.