These are a really common fuse type, the Brennzünder 39. You first start seeing these on the E39 egg grenades but later they turn up on everything including the M43 stick grenades as well as the late-war improvised grenades and explosives.
The igniter (Brennzünder 39) consists of a short brass or steel body, screw-threaded at the head to receive a square nut and the ball cap and at the base for insertion in the bush. An internal screw thread is formed in the base end to receive the delay unit. The body contains a friction composition through which passes the pull wire. The lower end of this wire is coiled to provide resistance to the pull. The upper end of the wire has a loop through which is threaded a two-and-a-quarter-inch length of cord. The cord at its outer end is attached to a loose washer within the ball cap. When the cap is screwed to the grenade the slack of the cord is stowed inside the cap. The delay unit consists of a short steel tube filled with compressed powder and is screw-threaded to receive the detonator. The igniter is packed and fitted with a molded transit cap in place of the detonator.
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