Abstract: A pivot-axis, pin arrangement for rifle receivers can serve as a trigger or hammer pin therefor. A lower housing has a pair of sidewalls defining a gap and with a pair of bores spaced across the gap. The outer side of one sidewall has a slightly recessed channel which is elongated between spaced ends, at least one of which is rounded and centered on the axes of the spaced bores. The pivot axis pin has a cylindrical shaft and a T-slot head style head. The head has one portion forming an annular ring while the remaining portion is elongated to an end. In use, the pin is inserted through the bores, and is ‘simply supported’ by the ends thereof in the bores therefor. The head of the pin locks against rotation merely by settling in into at least one rounded end of the recessed channel.