243 WIN arbor for use with 223 boresight. This arbor will laser bore sight any 308 Winchester based calibers. Also fits military 7.62-51 chambers. 
 
Calibers it will fit:
243 WIN
308 WIN
7MM-08
260 REM
338 FED
256 WIN 
358 WIN
307 WIN
7.62 X 54R
7.62 X 51
444 MARLIN
356 WIN
7MM STE