This is a set of shims for the barrel block to receiver (fork).
Over time, some of the B18/B19 series rifles (Phantom, Quest, Optimus, Summit, Vantage, Trail NP, Classic .22, Tac-1, G1, etc.) can develop some slop in the barrel bushings and/or side-to-side movement in the barrel.
This is the solution- 4 shims than can be installed to fit your precise requirements. Two shims are 0.60", two are 0.65" (stock plastic bushings are 0.060").
These bushings are made from aluminum to hold their rigidity, but wear out before the barrel block or tube forks wear (which would be alot more costly than replacing shims after 25000 shots).
Note: Some sanding will be required on the barrel block to fit the shims for a flush installation. Two sizes are included to allow for exact spacing as required by your specific rifle.