This is where I have split loyalties: the straplock manufacturers design their gadgets to work nicely. Well, let's suppose they all do, for a moment. They design them not to come loose. This, unless I've become vaguely confused, is the purpose of a straplock - to not come loose.
Now, a standard strap is designed to fit over a standard button - they have probably varied a bit over the years, but that mushroom-headed post is pretty much the norm. You punch a quarter-of-an-inch hole into the strap and cut a short slit running into it and it works.
(Except, of course, for the reason I give HERE - the reason for these articles in the first place]
¼" = 6·5mm
If you were a designer looking for a more modern method of securely attaching a strap to a guitar, (obviously with some form of locking clamp), it might occur to you to use a larger hole. From an engineering point of view, you might think, ten millimetres (a convenient, common tool size) must give a more substantial section of strap-end for your lock to sit in - the increased circumference spreads the load, as the logic might go.
Well then, in that case we must be depending on the edge of the hole to support the weight.
Really? We are talking leather or soft plastics here, not metals. My experience tells me that any relatively narrow bolt or rod passed through a flexible material will distort that material if a weight is hung from it. Surely that's the job of the clamping faces - to distribute the load and support the material.
My conclusion is that it's merely convenient - read cheaper - to use a standard metric diameter. Stuff everybody with a classic instrument, they'll just have to get it modified or bodge the fitting.
An altermative - as seen in the Fender 'f'-series - is to use a fixing that will fit the standard hole and then to ensure that a generous area of the strap is gripped between the faces of the the two parts of the lock. They're still not perfect - see Fitting Staplocks.
If you've followed this so far, this is the key engineering point. If you can spread the load over a relatively large area of strap surface and grip it tightly, it doesn't really matter how big the bolt is - within reason - as long as it is strong enough for the job. A quarter-inch bolt is quite sufficient and if cut with a fine thread can generate a serious amount of pressure, even when merely hand-tightened.
If musicians are faced with having to modify their strap to accomodate a larger bolt, a lot of them aren't going to do that. Instead, they'll just force it through the standard hole. Works OK. -ish. Except the lock won't sit evenly on the leather, consequently won't grip it properly and will tend to come loose. So the straplock is then a waste of time, money and space.
It's easy to punch a bigger hole in the strap. If you have the right tool. Yes, it's called a hole punch. I use them a lot. Doubt that Johnny B. Goode bothered carrying one in his gunny sack, though. (See 'Make or Enlarge a Hole in Leather')
So, in the course of writing this series of articles, I think that I've convinced myself that I favour straplocks that don't require permanent modifications to the strap - or to the guitar, come to that. But if you happen to favour a straplock that DOES need bigger holes, I'll make it so. A small leather 'washer' can always be made to fill the gap if you change your favourite later. Not super-elegant in engineering terms, but invisible.
Technophobe May 2013
I'll probably come back to this again.
PS December 27th 2013 - I have already. Now two pages, with extra comments.
Slight edits January 5th 2014, February 28th 2014
Straplocks Pages / Articles
Return comments, by the way, can be sent HERE.
Haven't set up a 'forum'-type section.
Not totally convinced that I want to - I'd have to maintain it and that drags me out of the workshop.
Maybe you'll convince me.