Text copied from TM-E 30-451, March 1945 :

This adapter serves the double purpose of connecting the cap and safety fuze, and permitting the cap to be screwed into a standard threaded charge.
It consists of a tube which covers the junction of the cap and fuze, and is enclosed in a bakelite cover.
At one end of this cover is an externally threaded sleeve; the other end is covered by a bakelite cap with a central hole for passage of the fuze, through a waterproofed fitting.

Early adapters were made of brass instead of bakelite.
The adapters were to be combined with "
sprengkapsel No.8".
Length: 53mm , diameter body: 16mm, diameter collar: 18mm