Music Man bass pickup with screw poles

[Alberto]

The thread inserts exist to replace stripped female threads in things like engine blocks. They are very much nonstandard threads (on the outside) that require a special tap. Normally the inserts are sold with their tap, Sensmag threaded alnico magnets might actually be a cheaper way to go. Of course you are threading into a rather soft material, forbon and if you drill the right sized hole in forbon the helicoils or sensemags will easily form their own threads. Helicoils are steel hence magnetic so they will change the sound possibly.
the M8x1.25 thread has a minor diameter of between 6.6mm and 6.9mm so your magnets couldn't exceed that...
Here's a table https://mdmetric.com/tech/LimitingDimensions.htm Unfortunately there aren't metric helicoils that have an internal thread dia that matches up will with any standard magnet sizes.
You could check SAE NSF thread charts to see if there's a good fit.

Thanks for your help David!

I have found some M10x1.25 helicoils (different brand but same use) sold without their tap, with an external diameter of 10.30mm and minor diameter of 8.647mm. I think 8.5mm diameter rods would fit (I can have them custom made by Cermag in the uk). I know that helicoils will raise the inductance of the coil and possibly change the sound. How much? This is something I will discover only when the pickup is ready, I guess.
I've contacted Sensmag as well but shipping costs to Italy are too high for such a small order.

On balance, it may be that the price I'm charging would only be enough to cover the cost of this prototype, but it's always nice to work on new projects!

[Jim Shine]

Are you making this pickup to work with the stock preamp? The 4K, is that what the current pickup reads? Is this an Ernie Ball era bass, or earlier?

FWIW, the earliest G&L pickups are lightly modified Music Man pickups (the first G&L guitars and basses are actually lightly modified Music Man Sabre's all around). You can grab some ideas of adjustable poles and such from those.

[Alberto]

Hi Jim, thanks for your advice! The customer is building a new custom bass. He asked me for a pickup with adjustable poles, a classic MM sound and same pickup dimensions (he's going to build a wood cover for it). I asked him why he needs adjustable poles and he replied that he likes them that way...

I'm oriented to use alnico rod magnets but G&L pickups may be a suitable alternative, I may even try to find one and modify it to suit my needs (are they still available somewhere?).

By the way, the customer didn't confirm the order yet, so I'm just collecting ideas...

[Jim Shine]

The only thing I am not 100% certain about is the bobbin sizes. I can't remember if Sabre basses had a narrower coil design for the bass. The guitars definitely had narrower coils. And G&L used Sabre sizes. I will have to dig for those details. I may also have the source of their adjustable pole parts somewhere. 99% of that info I have is CLF Research era, but that bleeds into early G&L.

[Alberto]

Thank you Jim,
I was waiting tor the customer to confirm the order, but he eventually disappeared! So the project is on standby at the moment...