Keeping Classics Pumping!
Used good shape, Carter powertube, non standard carter style valve retaining screw, wear on aluminum valve retaining screw and cup seal, lapco cup seal, 8x32 threads id=.200, .125? id for 3 base holes.
The Valve retaining screw on this Carter powertube is 5/8 inches x 18 threads per inch (tpi). Standard nelson valve retaining screws are 9/16 inches x18 tpi.
Some newer carters may use valve retaining screws that are 5/8 inches by 20 tpi. And checkout this thread on mcb for more information on Carter Power Tube Valve Retaining Screws