WW2 M1 M2 Airborne Paratrooper Helmet Fixed 'D' Bales
These are a set of reproduction fixed bales (or 'D' bales), as used on the American M2 Airborne helmet in WW2. They are made to the correct size and finish which is steel, which means they will rust if left in wet conditions - just like the originals! Stainless steel M2 D bales were not made in WW2.
If you have a swivel bale then all you need to do to convert to a fixed bale is to grind off the swivels and spot weld the new bales. Instructions here.