Fishman Full Circle Sizing FAQ
Which size do I need?
The Full Circle Pickup from Fishman is offered in three different thread sizes, since not all bridges use the same sized adjuster wheels. Of the choices, the SAE ¼x20 is the most common bolt size by far. Almost all of the adjustable bridges we've ever sold at Gollihur Music have been of this size.
The easiest and most fool-proof way to tell which size you need is to take out your current adjuster wheel and count how many threads there are in a ½ inch along its threaded edge (since the wheel doesn't quite have a full inch of threads). If this measurement shows that your current bridge has 10 threads per half inch (20 threads per inch), similar to the graphic at right, you need the SAE 1/4"-20 version of the Full Circle. If it has 9 threads in a half inch (18 per inch) than it's possible you have the new 5/16"-18 version. (You can double-check by measuring the end diameter of the threaded post - the new version is threaded onto a larger post, 5/16".)
If you aren't even close to 20 threads per inch, try counting threads next to a metric ruler - if the threads are spaced exactly one millimeter apart, you've got a metric-threaded bridge (and need the 6x1mm version of the Full Circle).
These printable gauges from Bolt Depot (a purveyor of hardware items) may also help you to count threads accurately.
If you are uncertain about the size, here's another tip: Go to a decent sized hardware store (e.g. Ace Hardware or True Value franchise) and visit their aisle with all the little drawers with all the different sized nuts, bolts, etc. Buy one or more nuts (usually less than 35 cents each) in the size you think is correct, remove the adjuster from your bridge, and see which size bolt fits.
Here's a photo of the adjusters side by side, for comparison.
|SAE ¼x20||means:||¼" post, threaded with 20 threads per inch|
|Metric 6x1mm||means:||6mm post, threaded with 1 thread per millimeter|
|SAE 5/16"x18||means:||5/8" post, threaded with 18 threads per inch|