FJ helmet spanner bolt questions

[Luftm40]

Two part question:

- Does anyone know why the late war bolts on FJ helmets were made in aluminum? Typically with other German items, aluminum is an early material, and steel later...very fascinating

- Can anyone post a picture of an original spanner wrench?..the kind that fit into the three holed early bolts.

[Willi Z.]

Can give it my best with the first part. Even then the spanner bolts rusted very quickly, making it tough for troops to loosen the bolts and replace/repair helmets. Aluminum was much easier to loosen......and the slots were easy to work with. Compared to the wrench needed for steel spanners. Was a practical matter, more than other items which went from aluminum to steel as the war progressed.

Willi

[Prosper Keating]

Willi is spot-on there. The pin wrench required for the early steel bolts wasn't a tool anyone other than the battalion quartermaster was likely to have. Sure, you could sprag - fine old spanner monkey term from England, that - the bolts with, say, the head of a bullet and loosen off the nut inside with a pliers or perhaps a spanner from an MG toolkit but there isn't much space for that. And tightening it all up again is a problem...which is why so many fell out, necessitating bits of wire etcetera to hold it all together, as we see in some photos.

Many people do not understand how nuts and bolts - or nuts and studs - actually work. Which is why, when doing a bit of DIY maintenance on your old car or motorbike, you often come across fasteners done up so tightly that the metal has begun to stretch or drastic measures are needed to get it loose. You have to think in terms of a fastener as a spring exerting tension on the components it holds together. This is why you should only tighten them slightly or to specific pound-per-square-inch values. "Just nip it up with two fingers on the spanner (that's wrench for you Yanks)", as they used to say. Pulling on any nut or bolt with a three-foot spanner will quickly exert several tons of end-load, the metal will stretch and the components on which it is bearing will compress. A short time later, your fastener will be loose again. Then you will do it up once more and the threads will strip.

OK? So...the short, champfered bolts and slim, wide shouldered nuts used on the FJ helmet would be fine, 'just nipped up' were they in a more stable, static environment. But they are not at all in a stable environment. Not only do they have to hold the liner to the shell, but they are also the bearing axes for the chin and neck straps. To get them to stay tight, you really need to clamp that nut and do the bolt up 'dead-tight', the old term for 'on the point of breaking' so that it won't move. And even then, given the operating conditions, the steel fasteners as used on FJ helmets are far from reliable. It could have been solved, perhaps, by making the bolt long enough to accept a locknut - which bears on the first nut, preventing it from movement - but this would have posed a risk to the wearer. Of course, they could have had the two nuts on the exterior but this might have been equally unacceptable to Luftwaffe safety officers in charge of parachuting.

So, a different material was needed. Aluminium, when used for fasteners or in other bearing applications, is also prone to sieze up like steel under field conditions. But it was clearly better in this particular application than the steel fasteners as less torque produces more end-load and, consequently, a fastener less likely to come loose as the various materials it is securing expand and contract, at different rates, depending on factors such as temperature. This is why, at a time when aluminium, a restricted strategic material by the middle of the war, was reserved principally for aircraft production and other essential applications, helmet manufacturers were allowed to use this metal for FJ helmet fasteners. I should mention that we are not talking about common-or-garden aluminium here. The nuts and bolts are made from aviation quality aluminium, a precursor of what we now call Dural. Very tough but springy stuff: just the thing for short, wide bolts and nuts that need to stay tight in far-from-ideal conditions like an FJ helmet.

I recall that when we still had the old WW2 type jump helmet in the British airborne - before we changed to the Kevlar helmet that saw experienced airborne soldiers collapsing from heat exhaustion on speed marches because of the total lack of ventilation! - the slot-head bolts and nuts holding the liners in were made of brass. We never had problems with them. Perhaps the Germans ought to have used brass. You can do it up very tightly without much pressure and it locks itself into place. A bit of heat from a Zippo usually enabled one to break the bond.

There you go...yet more useless information!

PK

[Luftm40]

Thanks Willi/Prosper. I knew the bit about needing a special wrench, and I'm sure these bolts were a pain the a#@. I can just imagine stopping for a break on road march, only to notice that a nut had fallen off, and one of your chin harnesses had detached. The Germans did, and still do, have a tendency to over engineer things...too many moving parts.