As shown in the photo, each threaded upper receiver includes a knurled thread protector and receiver pin assembly (bolt assembly and cocking knobs not included). The threaded barrel is ½ x 28. If the threaded upper receiver is purchased that matches the caliber of the of the vz. 61 pistol, the original bolt assembly can be used with the upper receiver. Since the vz. 61 does not use a locking mechanism, headspace is not applicable.
Only 7.65 mm (.32 ACP) Browning upper receivers can be used on 7.65 mm Browning vz. 61 lower receivers. It is not possible to use a .380 upper receiver or 9 mm Makarov upper receiver on a 7.65 mm Browning vz. 61 lower receiver. Reason: the 7.65 mm Browning (.32 ACP) vz. 61 magazine well will not function with .380 or 9 mm Makarov magazines.
