Bayonet Cap lampholders have a thread in the cap or base which can be used to mount to a male thread. There is 10mm and 1/2” variations available in these BC lampholders. B22 Lampholders have a porcelain insert which is used to turn the wonderful lampholder on. Lampspares also has a Stem Locking BC | B22 | Bayonet cap lampholder which has a screw in the base, adding an extra safety feature in the lampholder.