Imperial thread heat set insert assorted set with 4-40, 6-32 and 8-32 thread types. There are three lengths of the 4-40 which are 0.135", 0.170" and 0.226"; two lengths of the 6-32 which are 0.150" and 0.281"; and three lengths of the 8-32 which are 0.185", 0.250" and 0.321". Each standard heat set insert size comes in a 20 pcs with 160 pcs in total making up the kit. The heat set inserts are made from brass and have a knurling to grip into the plastic part. These english heat set inserts work on all types of thermoplastic whether that is injection molded or 3D printed plastic parts.