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Fitting a Fishman Full Circle when the threads don't match

Discussion in 'Amps, Mics & Pickups [DB]' started by macmrkt, Jul 26, 2005.

  1. macmrkt

    macmrkt Banned

    Dec 4, 2002
    I wanted to change my AES and New Standard Bass DB's to Fishman FC pickups. However, the stock bridges were drilled for adjusters that are 5/16" thread while the FC comes with 1/4" threads. On a tip from Arnold Schnitzer, I was able to 'retap' the holes using a Helicoil kit, commonly found in auto supply stores. Essentially you end up with a steel threaded insert that fills the the 5/16" hole and converts it to a 1/4" thread. It worked out fine. I'm not sure it would work on a hole that's bigger than 5/16". However, if you need to make this transition, you can do it. There are a few tips to make this a smooth process that I can post if anyone needs them...
  2. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Please do - this is a question that I've been asked many times by lurkers who email me, and I never know what to tell them. Post the tips, and I'll stick this sucker in the "Newbie Links".
  3. macmrkt

    macmrkt Banned

    Dec 4, 2002
    To do this properly, you have to feel comfortable taking off your bridge and working with tools. The working time for this job is only about 20 minutes.

    You'll need a Helicoil Kit for 1/4-20 threads. Sold in auto supply stores. Also, get the matching drill bit while you are there, unless you have the 17/64" size that's required (it is indicated in the Helicoil kit, but not supplied). You'll spend about $30, but you get enough insert threads to do 3 basses (or a few valve covers!) Then read all the instructions with the Helicoil (not much) and the Fishman (you can skip the parts about cutting a new bridge).

    1. Mark the position of your bridge's feet with painter's masking tape if you are not sure of the exact position to replace the bridge later.
    2. Lay your DB down in a padded work area with the bridge up. Put a weight over the soundpost area of the table (top of bass) and loosen the strings.
    3. Carefully slide out the bridge.
    4. Separate the feet of the bridge and remove the adjusters.
    5. Do your test fits and see how all the pieces will work together. I'm assuming you are going to rethread the part of your bridge that was previously threaded. There is a sound difference depending on if the threads go up into the bridge or down. It seems to be OK if there is 'play' in the hole on the non-thread side, but you must have these non-thread sides of the Fishman adjusters in complete contact with the bridge. See the Fishman's instructions for more info.
    6. With the 17/64" bit, drill the bridge or feet where you will be inserting your new threads. You only need to go in as far as the depth of the Fishman adjuster thread. I found that a exisitng 5/16" hole was so close to 17/64" that I could just spin the bit by hand (gloves please!) without even needing a drill.
    7. Create the new threads by using the supplied Helicoil tap tool. This can be done mostly by hand (did I say gloves?). For a bit of extra turning strength as you get to the end of the hole, I found one of the sockets from my socket set fit over the end of the tap nicely and was easy to drive with a hand socket tool.
    8. Thread a new steel insert (what Helicoil refers to as their replacement threads) fully onto the supplied Helicoil tool (this tool is called a 'mandrel'.) Put the mandrel/insert into the hole by screwing it in. Apply a little force and be sure to go in straight. Stop when you get the top of the insert to be a 1/4 to 1/2 turn below the surface of the wood.
    9. You can stop at this point and call it a day. The Helicoil is so strong that even its 6 threads is good enough to hold the new adjuster. That's because studies show that the first 3 threads hold 90% of the force of a screw. With 6 threads covering the adjuster, that's enough for most people. But if you are a perfectionist like me, you may want to stack another insert inside to have complete coverage of the adjuster thread. This is trickier. You were warned.
    10. To add another insert, you'll first have to turn the first insert down to the exact point inside the hole to accept another insert on top. Measure an insert and screw the first insert to that point plus 1/4 turn. Add the second insert above it as in step 8. Stop when you feel resistance and go no further.
    11. You'll now have to break the 'tang' or the bent part at the bottom of the insert. Rest the part of the bridge that has the insert on a heavy solid surface covered with a towel. Find a small nail set or hole punch that's thin enough to go inside the inserts but with a blunt enough point so it will rest securely on the top tang you'll be breaking. I used a nail set. Rest the tip of the nail set or punch on the top tang. With a hammer, tap the set or punch one time with a light to medium power stroke (I used a 20oz hammer). The tang will break right off.
    12. Follow the Fishman instructions to complete the pickup insertion. Remount your bridge as it was originally set (in all geometric planes I might add!) and retighten your strings. Don't forget to remove the weight before you stand your bass up!
  4. Jazzman


    Nov 26, 2002
    Raleigh, NC
    I have been wondering for years why most people don't put helicoils in when doing an adjustable bridge. It just makes sense unless your adjusters are wood.
  5. jstiel

    jstiel Jim Stiel

    Jun 5, 2004
    Lake Orion, MI

    Here are a set of adjusters that seem to use the same principle.


    I would imagine the metal-to-metal threads of the Helicore set up would allow nice easy turns. Do they?
  6. macmrkt

    macmrkt Banned

    Dec 4, 2002
    I don't really feel that it's any easier to turn when I compare my setups with and without. That may be due to the fact that it took me a few tries to get the procedure correct and along the way I made mistakes so my threads aren't perfectly clean. The aluminum adjuster threads are very soft and easily get mucked up. The advantage though is that if you do a really rotten installation, you can force the aluminum to go in anyway!
  7. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
    I have some bridges with threaded inserts, with metric threads and matching wheels. They are a little easier to turn with the strings at tension, but the pressure from the strings is pretty substantial and I'd still recommend loosening them enough to make it less of a finger-abrading effort.
  8. macmrkt

    macmrkt Banned

    Dec 4, 2002
    I might add I got all 3 of my Fishman's for this bass chainsawing project from Bob with flawless fast delivery. Knowing he was on the other end helped to make this somewhat nerve-racking and knuckle-knocking project a bit more bareable (Or is it bear-able. Or beer-able?).
  9. arseniotall


    Dec 24, 2005
    anybody ever try this coming from Kolstein wood adjusters? Would i need the same Helicoil size?