These are the Dual EZ-Thumber thumb stud system. This dual stud design is one of the most secure and professional looking on the market today. It can be used as a stand-alone style stud or as a thumber-stop, using the frame/bolster as the blade stop.
To use this thumbstud system, drill a 3/16" hole through the blade. Then screw the two halves of the thumber heads into each other using the 6-32 threaded rod (included). These fit through the blade and tighten up strong! Assembly requires Allen wrench, probe and pliers.
These are popular upgrade thumb studs.
DREZTH250-D = Medium (Dual)
.250 head x .185 step x 6-32 thread