Roly has found this text on the net, this might be it.
Who can confirm?
UZRG - with "closed top". Delay tube can be brass and from pressed powder iron.
UZRGM - with "open top". Delay tube can be brass and from pressed powder iron.
UZRGM-2 - with aluminium delay tube; handle have different length from nail hat to safety pin (almost 1mm) and holes for safety pin not match; handle can have big hole and mark UZRGM-2. In delay tube used different ignition composition.
There is also a post-war practice version of this fuze, which had a replaceable black-powder charge.
SEE THIS LINK