This post is to clarify some questions brought up in the 155mm discussion. The fuze sizes for MOST of the US Artillery from 75mm on up for the treaded portion were about 2" measured from the tops of the pitch and with 12 threads per inch. There were exceptions to this rule when dealing with the WP rounds of 75mm, 90mm and 4.2". They were 1.7"x14 . For PD these would have been the M48 Series. Now, take that same fuze and add a booster adapter M21 series that has an arming delay and a healthy booster (gaine) on it and has the 2"x12 thread pitch, and you have the M51 series PD fuze. The Navy even used it in the Mod 3 version for 5" 38 Cal. All of this was to make things as standard as possible so we could mass produce as much as possible and get it to the front. If you look in the NAVSEAOP 1666/TM 9-1985-3 you’ll see what a headache the Germans had when dealing with fuzes and rounds. We kept with this standardization as much as possible till even now, with the M577/M582 series MTSQ and the M739/M739A1 PD fuzes.
The M577 and M582 are almost identical but the M577 is used for "payload" rounds that have an ejection charge and the M582 has a booster screwed to the base so it can be used for HE and WP rounds. This helps simplify production and procurement. That's a starter to get discussion going.