Standard M10 thread 
great grip! 
also available for unthreaded
Our non-slip threaded rubber ball (MSRP $16 for the threaded ball, $9 for the unthreaded rubber ball without the threaded insert)fits all M10 threaded endpins, and can also be purchased separately with or without the Delrin threaded insert. The hole in the unthreaded ball is just under 5/8ths of an inch in diameter. It offers a secure unglued fit on 3/4 and 11/16th inch dowels and rods, or a secure glued fit on 5/8 inch rods.
