The 15960 target holders are designed to work with the Brunson Invar System. On one end, a 3/8"-24 external thread mates to our standard Invar System tubing. The other end provides a slip-fit holder for targets having either a 6mm or a 1/4" diameter shank. A brass thumbscrew allows you to secure the target without gouging the shank. Several different configurations of this target holder are available. Using the table below, choose desired values for A (offset) and B (bore diameter). This item is supplied with a spare thumbscrew. You may wish to read about our other Invar System Components as well.