This is some of the best urethane material for thumb inserts. As a ball driller, I find this a great material to drill and carve! Aside from the JoPo thumb urethane removable inserts this is one very good unit. When I drill bowling balls with finger and thumb inserts I will try to match all three. However, if you want a contrast or a specific color please make sure you make that selection. Typically, there would be one insert per ball – these inserts are glued into the bowling ball.