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blakkshepeaudio 3rd March 2012 11:46 PM

Horns and Compression Drivers - Screw thread too tight

A while ago I bought some horn flares with 1 3/8 inch screw threads. They were cheap and I thought they might come in handy.

Today I bought some cheap piezo drivers (3 different kinds to play with) planning to screw them into the flares and take some measurements to see if they were any good. Party speakers maybe.

Well, the threads are so tight that I could only screw the first one in about half way. The effort required to UNscrew it was so great the body of the piezo driver broke off in my hand. One driver down and a horn flare with half a tweeter jammed permanently into it. Boo.

So I tried a different driver, very carefully, in another horn. Same deal. So I carefully unscrewed it, applied some vaseline and tried again. Went in easily, about half way, then stopped. Very carefully unscrewed it again, with much effort.

I have now tried half a dozen driver / flare combinations, all the same.

There are no obvious defects in the threads of the drivers or the flares.

Can an experienced soul tell me if this is par for the course (plastic driver thread into plastic horn thread) and if so, what's the trick to getting them in and out.

If this is unusual, perhaps someone might suggest a fix.
Perhaps I just bought dud flares, which is pretty sad because I have dozens of them.

Any advice gratefully received.


qusp 4th March 2012 02:29 AM

maybe you are experiencing some sort of metric vs the neanderthals issue? =D

blakkshepeaudio 4th March 2012 04:08 AM


Originally Posted by qusp (
maybe you are experiencing some sort of metric vs the neanderthals issue? =D

If that's the case, it looks like the Neanderthals have got this one in the bag......

qusp 4th March 2012 04:59 AM

damn throwbacks

seriously though, i reckon thats your problem as thats how it goes with using for example M3 into a 4/40 thread, it'll go in a bit if you force it, but never all the way and you ruin the thread in the process

454Casull 4th March 2012 05:21 AM

Are all units using 1.375"x18 thread?

blakkshepeaudio 4th March 2012 05:56 AM


Originally Posted by 454Casull (
Are all units using 1.375"x18 thread?

Uh-oh. In my ignorance I was unaware that there was more than one standard. This would explain my dilemma but surely there aren't multiple TPIs in use in this horn / driver application - that would be completely insane.

Please tell me it isn't so.....

454Casull 4th March 2012 06:33 AM

They should be.

Problem is, nobody makes a tap and die in that size in case you wanted to clean up the threads.

w_oswald 4th March 2012 06:40 AM

Hi, Blakk:
Hmmm, maybe the plastic horn flares were cheap for a reason? If the threads are moulded instead of cut (machined) I could see plastic - or "Resin" as it's fashionably called nowadays by marketing types - shrinkage being the cause of your problem. I got myself a Go/No-Go plug gauge for 1-3/8-18 UNEF threads, and it runs easily into any threaded horn that I've tried it on. I've never come across a tapered variant of that thread, and don't know of any standard to that effect either.

If you can get a couple of threads engagement before it binds, why not just make up a spacer you can drop into the threaded hole, thick enough to let the driver's end face butt up against it before the threads bind up? I've seen cork or rubber washers typically used in that location, or maybe you could find a bit of hard plastic tubing of the right ID/OD and just measure and cut the required length.

Hope this helps!

blakkshepeaudio 4th March 2012 07:57 AM

Thanks Wilf, that is an ingenious suggestion! Not sure how it might affect performance though.

454Casull, damn, that was my next idea, buy a tap and die and tidy up the threads that way. Sounds like that's out, although I might try some machinery suppliers just on the off chance.

I am thinking of buying some new flares and making an outdoor water scuplture out of these....

Waddya think?

el Blakko

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