Perhaps I should have chosen my wording better.
But I will, in a sense , stick with the idea of the all steel fuze being use to protect the threads. I say that because one of my prized items is a 5-inch antiaircraft, common, mark 35, model 10, Minneapolis-Moline Plant projectile that was given to me by a former neighbor, Hap (Hubert) Welch, who was on the production line and actually was involved in the production of the projectile. It has a solid steel "dummy" fuze (as shown on the projectile in question above) and a threaded steel plug is in the base tracer/ fuze well. Hap said this was done to protect the threads while the projectiles were in shipment, via the railroad, to a separate explosives loading facility. Below is a short history on the projectile I have, that Hap and I wrote together back in 1999, shortly before he passed away.
5 inch Navy Projectile
Produced at the Minneapolis-Moline
Como Ordnance Plant
(Minneapolis-Moline Power Implement Company)
World War II
In 1945 near the end of WWII the U.S. Navy canceled many orders for ordnance. When this happened at the Como Ordnance Plant, workers were offered the chance to take a projectile from the production line as a souvenir of their efforts in helping to win the war. One of the workers was Hap (Hubert) Welch who picked this projectile as his war memento on the last day of production. Hap began working on the "5-inch" line in mid-1944. His job was running a lathe that cut and shaped the copper driving band and gas seal located near the base of the projectile. Besides manufacturing various tractors used to pull military equipment and 5-inch projectiles Hap indicated that the Como plant also produced Navy 6 inch and Army 155mm projectiles. The plant was located on Como Ave. in St. Paul, Minnesota.
Hap's description of the production line for the Navy 5-inch projectile-
Long bars of steel, approximately 2 to 3 inches square were shipped to the plant. These bars were sheared into sections around 24 inches in length. "You always knew when the shear was in operation since the entire floor of the building shook and there was a loud 'thud' with each section cut." The resulting short bars were sent to a furnace and heated orange hot. From there each heated bar moved through a series of rams that compressed the bar lengthwise until the steel was formed into a billet slightly larger in diameter than the actual projectile. A cavity was bored in the billet and in turn an inside lathe enlarged the cavity to the proper size. The outside of the billet was cut to size on a lathe and another lathe cut a grove for the copper band. Then a band was slipped onto the projectile and pressed into place. During the final lathe work the driving band/gas seal was formed from the band. Fuse and tracer wells were then threaded; a solid steel dummy fuse and a steel tracer/fuze well threaded plug were screwed into each projectile to protect the threads during shipment. Finally the projectiles were prepared for shipment to another facility to be charged with explosives.
Markings on the base of this projectile: 5IN AA COM MK 35 MOD. 10 MMP 37LOT.
Translation: 5-inch antiaircraft, common, mark 35, model 10, Minneapolis-Moline Plant, 37th lot.