[CompClassics]

The belt hardware was derived from military surplus, the markings are as follows....

1) early hardware was "AN" & "OTT" marked and would have been available as surplus to the civilian market earlier than "MS" part numbered components.

2) later hardware was "MS" marked and post "AN".

The "AN" markings stood for "Army / Navy" acceptance and the "MS" stood for Military Standard which is still in use today for parts made for military applications.