Sometimes there are laser keychains on ebay. They are the same units as the GTA lasers without the shaft mount, but a key ring(chop it off). They cost a few bucks plus shipping. If you buy 5 or 6, the shipping is combined. extra batteries.
With some small pieces of duct tape and the small lasers, You can not only check the shaft.... but forearm, PP alignments... the angle of your FWs... think your head is stationary? tuck (not tape) one behind your ear .....
Threaded Mode
