You are looking at a newly manufactured Tasco range finding trajectory compensating cam lock nut. We have made improvements to the old style ones that came with the scopes from Tasco. These have been fashioned from high quality harden aluminum, to make them harder to strip. We have also made the o-ring heaver duty to help keep them from loosening dury use. They will replace the original ones perfectly and you can paint them black to match your scope. This is a chance to put that Tasco TR BDC scope back in use.
This part screws to the cam stud to lock it down.
List of some of the Tasco scopes these fit. Tasco 3x20 #7485 c5 (A-56
Tasco 4-16x40 #TR416x40
Tasco 3-9 x #629TR
3-9x40 wide view #TR39x40WA A059 8