UBASS end pin jack thread size?

the.waz

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Does anyone know the thread size of the end pin jack in a Kala UBASS, particularly the larger diameter part? On mine, the inside nut has always wiggled loose when I play with a strap, which is annoying but tolerable (I just open the access panel and tighten it). But lately I've started having a worse problem. Sometimes when pulling out a tight cable or removing the strap, it will abruptly loosen, and I think it may be actually skipping a thread, not just rotating on me. Indeed, when I remove the whole jack and wiggle the inside nut, it doesn't just slide but there is quite a bit of play in it. Surely it's not the wrong size nut, but maybe the threads are worn? I'd like to try replacing it with a thicker nut and maybe replace the lock washer and/or add some threadlocker when I reassemble it.

So yeah... anyone know the thread size? I would also accept someone saying I'm missing something simple and illuminating me. I have the nut, lock washer, flat washer in that order.

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I don’t know the thread size, but I can tell you what I would do in this situation. I’d take one of the large washers to a hardware store and get a matching lock washer. That should keep it in place.
 
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My advice is for the future is to remove the jackplug gently. I've recently had to replace an end pin jack (female) from a yamaha bass guitar. The owner experienced an intermittent on and off, whilst playing. We also noticed that quite a bit of "pushing was needed to bring the jack plug in position. We first tried tightening, which worked for a while, and there after the fault recurred . We removed the entire plug, and stripped it, to find that the plastic insulation had collapsed inside the chrome housing. A new unit was purchased and re-fitted. Customer happy.:cool:
 
Assuming the jack is the same as a Switchcraft 151 the nut is 15/32-32

You know what they say about assumptions though...
 
Try it with two nuts on the inside, so you can jam them together. That will lock them in place and keep them from spinning back off. The inside nut is really there to set the "depth" to accommodate the thickness of the tail block - the outside nut, under the trim piece, is what really holds the jack in place. If you don't have the inside nut threaded to the right position, the larger-diameter portion can stick out past the outside surface of the instrument, making it impossible to tighten the outside nut enough to clamp down on the tailblock (because it bottoms out against that shoulder where the smaller and larger diameters meet). Often when someone brings in an instrument complaining that they can't get the jack tight, or it constantly loosens, it's because of this.

Also - make sure the cable is being inserted and pulled out with a straight motion, not twisting or wiggling. That seems to be the other main contributor to people who have trouble keeping jacks tight - they're unconsciously twisting or wiggling the cable when they insert or remote it.
And yeah, the nuts are really thin and don't have many threads - it's pretty easy to strip them or overtighten them to the point that they skip.
 
Thanks, everyone, for the suggestions. I never was able to confirm the thread. I took the nut to a local hardware store but couldn't find anything close to a match. And 15/32-32 is believable, but I didn't feel like ordering hardware. Before going to threadlocker, I decided to try wrapping the jack with some thread-seal tape (the white Teflon tape for plumbing joints) to make the nut more snug... and it seems to have worked! At least, I unplugged and replugged a number of times without loosening or skipping. Time will tell.

The inside nut is really there to set the "depth" to accommodate the thickness of the tail block - the outside nut, under the trim piece, is what really holds the jack in place. If you don't have the inside nut threaded to the right position, the larger-diameter portion can stick out past the outside surface of the instrument, making it impossible to tighten the outside nut enough to clamp down on the tailblock.

dwizum, your descriptions are remarkably clear without a picture! This is more toward my first issue (spinning loose) than the second (skipping), but I took your advice on it. In the past I have tried to set the jack where the shoulder is just below the outside surface of tail, and that might not have been giving me enough room to really compress and clamp with the outside nut. So far so good; now my strap is just making the little outside cap come loose instead of the whole jack (improvements!).
 
Endpin jacks can be really frustrating. You have to install them semi-blind most of the time. Straps twist them loose, players twist them loose plugging and unplugging the cable, and it's all held together by wimpy little thin nuts with barely two threads in them! Worst of all, since the contacts that conduct to the cable are "inside" the barrel, if they get worn or dirty you have to just replace the whole thing instead of being able to clean or bend them like you can on a "normal" open guitar jack.

I really hate the things, if you can't tell... ;)

The 15/32-32 thread is used on some other common guitar hardware so I tend to always have spare nuts and washers around. If you end up still having problems, you might want to ask at a local music store or your local tech to see if they have spare hardware, since you couldn't find one at the hardware store. Or worst case you could buy a new jack for $10 or so and take the nuts off it.
 
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