The Finjak works on front-tab fins, but I designed it for rear tab fins. If you’re using it on a front tab fin and you hit something in the water, it could release, especially on longer fins. This can be a good thing, saving a broken fin or box, (or person). It’s a good practice to check your board whenever you hit something, but especially important when using a front-tab fin.
Bill Bahne introduced his Fins Unlimited box in 1971, and the Bahne-based removable/ adjustable fin system remains the standard for classic single-fin and 2+1 equipped surfboards and stand-up paddleboards.