Mounting ears : Finding the right screw size for pre-drilled holes

zortation

zortation

Dec 26, 2011
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#1
I've got an old amp that came with the ears un-installed. I try to put them on but discover that some yutz at the factory used the wrong size tap for the mounting holes on the amp, the thread holes are too big and the supplied screws just keep going in circles. The screws are the original screws for the amp.

How do I find out what thread size is in the hole?
 
#5
zortation said:
I've got an old amp that came with the ears un-installed. I try to put them on but discover that some yutz at the factory used the wrong size tap for the mounting holes on the amp, the thread holes are too big and the supplied screws just keep going in circles. The screws are the original screws for the amp.

How do I find out what thread size is in the hole?
Click to expand...
The other possibility, I think more likely, is some yutz supplied the wrong screws with the ears. You might first try to find out what screws were supposed to be used and compare that with what you have since it's a whole lot easier to measure screws than threads.
 
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#7
With metric threads I think you mainly find the 'fine' pitch variety.

If you have to take a stab at it you could measure the size of the hole. Across between opposite tips of the threads will be slightly smaller than the nominal bolt size, by about the pitch of the thread.
 
#8
15890642063555497129787007506454.jpg
Theyre 10-32
Likely the same pitch as the rack rails you'll be using. The threaded portion is shallow, 3/16 to 1/4"
15890643286316761558934811577391.jpg
15890643286316761558934811577391.jpg
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#10
Also beware that M5-0.8 and 10-32UNF are extremely close to one another. They might match if the nut is just a few threads deep, but then jam up if you go further. One of my rules from repairing a lot of bikes is to make sure a fastener can be threaded all the way on with the fingers before using any tools.
 
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#11
fdeck said:
Also beware that M5-0.8 and 10-32UNF are extremely close to one another. They might match if the nut is just a few threads deep, but then jam up if you go further. One of my rules from repairing a lot of bikes is to make sure a fastener can be threaded all the way on with the fingers before using any tools.
Click to expand...
Begs the question of @rufus.K whether it's a dead certainty

agedhorse said:
Be VERY careful with the length, especially on the right hand side.
Click to expand...

Is that stage right or amp left?
 
#14
I've seen guys drive screws into transformer windings, circuit boards and wiring harnesses by putting screws back in the wrong places, or using aftermarket generic screws that were too long.

A good way to check length is thread it in until the threads catch; then measure how much more threads there are between the panel and the screw head. Anything more than 3/16" or 5mm is potentially too long.
 
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#17
The supplied screws might have been intended for mounting the ears to the rack. Some racks have threaded rails.

Check that the rack ears are indeed the correct ones. The three holes should align on both the ears and the case.

Use a toothpick or to gauge the available depth inside the cabinet or take the cover off and look.
 
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#18
Seems like it would be easy enough to check in with Aguilar for proper screw diameter, thread pitch, and length.
If I had to guess, I would start with a US thread (only because they are a US company which is no guarantee), and buy a fine and coarse thread at you local neighborhood hardware store with the appropriate diameter. May as well buy a metric screw as well. As per fdeck, gently thread the screw in knowing that two of them are wrong.
As far as length, a general rule of thumb is go 1 1/2 time the diameter of the screw for the exposed section going into the amp. This needs to take material thickness and any flat or lock washers into the equation.
Better yet, pull the lid after you've discharged the capacitors or. unplug and don't turn power up for 24 hours before popping the top.
 
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