When you read the data sheet that NABOB posted, you will notice that multiple stem lengths are mentioned. There are three lengths of this type of long delay fuze or standard tail fuze and multiple time delays for each length, each with their own model number. The different lengths place the spinner in the proper location inside the tail, so the airflow arms the fuze. The fuze you show is the shortest and was used on the 100 Lb. and 250 Lb. bombs. The fuzes with the medium length stems were used on the 500 Lb. and 1,000 Lb. bombs, and the fuzes with the longest stem were used on the 2,000 Lb. GP bombs.
The two balls in a ramped groove on your fuze indicate that it is a booby-trapped long delay antiwithdrawl fuze, designed to function if anyone tries to unscrew the fuze from the bomb. When the fuze is screwed in, the balls rotate into the deep part of the ramp with no resistance. If an attempt is made to unscrew the fuze, the balls ride up the ramp and wedge themselves against the fuzewell, and then the rest of the fuze unscrews in the middle, which causes the fuze to function detonating the bomb.
If you ever want to install your fuze in a bomb for display, remove the piece with the balls first, or you will never see it again.