This is a really nice, quality 6 inch inside lock-joint caliper with the fine adjustment feature much like the Starrett No. 39, except the fine adjustment thumbscrew is side mounted, unlike the Starrett which is top mounted. This one is marked "COASTBILT". This inside caliper is in great shape well kept, the joint is lubricated, no rust, some minor staining of the bright polished steel, no damage, all threads and handware works correctly.  Features the lock down joint, and fine adjustment knob a bit further down, all in very good working order. This is a fairly rare maker's name, but I will rate the quality of this caliper as competitive to the Starrett model mentioned earlier.