What Size Allen Key?

guitarjack66 · February 2022

My Squier/Fender Jumbo acoustic needs it's truss rod adjusting but I have no idea what size allen key is the right one. Anybody direct me to somewhere I can find out please?

Soupman · February 2022

Different brand I know, but my Lowden & my Flambeau both use 5mm keys. A set of keys around this would cover you - they're not very expensive.

Mellish · February 2022

I think you need a 4mm Allen key mate but wait for others to confirm. Though as @Soupman says, anything going from 3-5mm will cover you in this case. Halfords, stores like that

Tannin · February 2022

Beware! Metric sizes and imperial sizes are almost but not quite the same. If it is imperial and you use a metric key, you can wind up with problems. Or vice-versa. Being a Fender, you expect them to use American (imperial) size parts. On the other hand, it was actually made somewhere in Asia, which suggests metric. Best to get the specs from Fender and be sure.

Tannin · February 2022

guitarjack66 · February 2022

Tannin said:

Beware! Metric sizes and imperial sizes are almost but not quite the same. If it is imperial and you use a metric key, you can wind up with problems. Or vice-versa. Being a Fender, you expect them to use American (imperial) size parts. On the other hand, it was actually made somewhere in Asia, which suggests metric. Best to get the specs from Fender and be sure.

Will check around. 1/8 or 1/16 seems to be fender standards.

ICBM · February 2022

A far-east-made Squier will be either 4mm or 5mm. Probably best to buy a basic set of metric keys even if you don't want a full metric/imperial set.

Most modern instruments use metric except for some US-made ones. The real danger as Tannin posted is using a 3mm key in a 1/8" socket - it's the biggest discrepancy and will almost certainly cause damage if you need to put any significant force on the key - it was a really poor design choice for Fender to use this size for something as critical as a truss rod, especially one where you can't easily replace the nut. This definitely won't apply to a Squier acoustic though.

Tannin · February 2022

ICBM said:

Most modern instruments use metric except for some US-made ones.

And, for some completely incomprehensible reason, Cole Clark requires a 3/8" socket. Australia has been fully metric since 1977 - 23 years before Cole Clark even existed - and nobody uses metric measurements for anything. Go figure.

ICBM · February 2022

Tannin said:

And, for some completely incomprehensible reason, Cole Clark requires a 3/8" socket.

Probably because Gibson do.

Tannin · February 2022

^ Ahh .... two veteran Maton workers start up a new Australian company more than 20 years after the phase-out of imperial sizes was complete, and they start making guitars that use Maton's nut width and neck profiles, but abandon the common 8mm Maton truss rod fitting in order to use the (relatively uncommon) Gibson one.

Yep. That makes sense.

Not.

(Do Gibson electrics use the same key? Electric Gibsons are common here (the acoustics less so), and Cole Clark started out making electrics alongside their acoustics. If so, that would explain it.)

BillDL · February 2022

Assuming your guitar has the hex socket for the truss rod inside the body rather than at the headstock, I would suggest that you loosen off the middle two strings when inserting and turning the Allen wrench. With the middle strings at full tension you are limited to a certain number of degrees clockwise and anti-clockwise and you would usually have to push those taut strings sidweways to make sure that the wrench is seated to its full depth in the hex socket. I once made the mistake of thinking I have the correct sized wrench firmly seated in the socket only to find that it was only part way in and was the wrong size. It slipped and rounded out the "corners" of the socket, but thankfully only where it had been pushed home part of the way. With the proper sized wrench pushed all the way in it still turned, but it gave me a fright and I learned my lesson. If only I had just loosened those middle two strings instead of using the key to push them aside I would have been able to feel that the key was the wrong size and wasn't inserted properly

guitarjack66 · February 2022

BillDL said:

Assuming your guitar has the hex socket for the truss rod inside the body rather than at the headstock, I would suggest that you loosen off the middle two strings when inserting and turning the Allen wrench. With the middle strings at full tension you are limited to a certain number of degrees clockwise and anti-clockwise and you would usually have to push those taut strings sidweways to make sure that the wrench is seated to its full depth in the hex socket. I once made the mistake of thinking I have the correct sized wrench firmly seated in the socket only to find that it was only part way in and was the wrong size. It slipped and rounded out the "corners" of the socket, but thankfully only where it had been pushed home part of the way. With the proper sized wrench pushed all the way in it still turned, but it gave me a fright and I learned my lesson. If only I had just loosened those middle two strings instead of using the key to push them aside I would have been able to feel that the key was the wrong size and wasn't inserted properly

Good advice. My problem is that the one hex key I have which might be the right size is from a repair set is way too short.

drofluf · February 2022

BillDL said:

Assuming your guitar has the hex socket for the truss rod inside the body rather than at the headstock, I would suggest that you loosen off the middle two strings when inserting and turning the Allen wrench. With the middle strings at full tension you are limited to a certain number of degrees clockwise and anti-clockwise and you would usually have to push those taut strings sidweways to make sure that the wrench is seated to its full depth in the hex socket….

Great piece of advice!

thanks

ICBM · February 2022

BillDL said:

Assuming your guitar has the hex socket for the truss rod inside the body rather than at the headstock, I would suggest that you loosen off the middle two strings when inserting and turning the Allen wrench. With the middle strings at full tension you are limited to a certain number of degrees clockwise and anti-clockwise and you would usually have to push those taut strings sidweways to make sure that the wrench is seated to its full depth in the hex socket.

Excellent advice. It also prevents damaging the windings on the G and D strings, which I still sometimes do even though I'm very aware of the problem and hold the strings out of the way with my fingers...

guitarjack66 said:

My problem is that the one hex key I have which might be the right size is from a repair set is way too short.

Use the long end, with a piece of stiff tubing over the short end so you can turn it.

BillDL · February 2022

If I get a guitar with a deeply positioned truss rod adjustment inside the body I do as ICBM has suggested, but rather than using a stiff piece of tubing I use an old push-on wooden file handle. I used to have a small screwdriver handle with a collet and a selection of bits. The collet could be tightened onto an interchangeable bit, whether it be a hex, torx or screwdriver bit, and I just tightened it onto the short end of an Allen wrench. Unfortunately I have misplaced it and haven't seen it for about 5 years. Time for you to go raking through toolboxes and bits-n-pieces boxes looking for a 3 or 4 inch piece of metal tube or thick-walled plastic tubing or similar.

BigPaulie · February 2022

guitarjack66 said:

BillDL said:

Assuming your guitar has the hex socket for the truss rod inside the body rather than at the headstock, I would suggest that you loosen off the middle two strings when inserting and turning the Allen wrench. With the middle strings at full tension you are limited to a certain number of degrees clockwise and anti-clockwise and you would usually have to push those taut strings sidweways to make sure that the wrench is seated to its full depth in the hex socket. I once made the mistake of thinking I have the correct sized wrench firmly seated in the socket only to find that it was only part way in and was the wrong size. It slipped and rounded out the "corners" of the socket, but thankfully only where it had been pushed home part of the way. With the proper sized wrench pushed all the way in it still turned, but it gave me a fright and I learned my lesson. If only I had just loosened those middle two strings instead of using the key to push them aside I would have been able to feel that the key was the wrong size and wasn't inserted properly

Good advice. My problem is that the one hex key I have which might be the right size is from a repair set is way too short.

Best to hold off until you've got the right tools. By a set of metric (I'd be very surprised if your Squier acoustic has an imperial nut) need keys. You can get a set for about £5 and they come in handy for so many other tasks.

guitarjack66 · February 2022

BigPaulie said:

guitarjack66 said:

BillDL said:

Assuming your guitar has the hex socket for the truss rod inside the body rather than at the headstock, I would suggest that you loosen off the middle two strings when inserting and turning the Allen wrench. With the middle strings at full tension you are limited to a certain number of degrees clockwise and anti-clockwise and you would usually have to push those taut strings sidweways to make sure that the wrench is seated to its full depth in the hex socket. I once made the mistake of thinking I have the correct sized wrench firmly seated in the socket only to find that it was only part way in and was the wrong size. It slipped and rounded out the "corners" of the socket, but thankfully only where it had been pushed home part of the way. With the proper sized wrench pushed all the way in it still turned, but it gave me a fright and I learned my lesson. If only I had just loosened those middle two strings instead of using the key to push them aside I would have been able to feel that the key was the wrong size and wasn't inserted properly

Good advice. My problem is that the one hex key I have which might be the right size is from a repair set is way too short.

Best to hold off until you've got the right tools. By a set of metric (I'd be very surprised if your Squier acoustic has an imperial nut) need keys. You can get a set for about £5 and they come in handy for so many other tasks.

Any links to typical sets? Just to repeat,the allen key I have doesn't have a 'long end.' Its just a stubby little thing. And yes you are correct in assuming the truss rod access is through the sound hole.

drofluf · February 2022

You can get long shafted ones; I have one for my Martin as the ones I have weren’t long enough.

Mellish · February 2022

You can also get a long-ended one with handle attached. I got one for my Martin. I think StewMac but not entirely sure. But to go for that you need to be sure of the exact size you need as they only come in singles

BillDL · February 2022

.... or just find a strong piece of tubing to slide over the short end to act as an extension and insert the long end into the truss rod adjustment socket, as suggested by ICBM earlier:

https://www.thefretboard.co.uk/discussion/comment/3197145/#Comment_3197145

Mellish · February 2022

With a Martin the long end of a normal 5mm hex is still too short, so you need a long pattern one to reach, at least with the dual action truss, though the OP might not with his guitar

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What Size Allen Key?

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