Fin Screw Length

bluefishz1 · Joined: 13 May 2012 Posts: 11

How do I determine the correct length to order for any given board? Should it stick out of the powerbox an exact amount? I assume it's the board size/make and not the fin size that matters. Thanks for your help!

zirtaeb · Joined: 03 Jul 2009 Posts: 1764

4-5 threads should be screwed into the power box base to make it tight.

westender · Joined: 02 Aug 2007 Posts: 478 Location: Portland / Gorge

You could poke a stick in the hole to see how long a screw you need. Got a hacksaw and file ? Or, screw it together to see how many extra threads you have left, then cut them off to make the 4 or 5 turns.

konajoe · Joined: 28 Feb 2010 Posts: 34

You are dealing with 3 variables:

1. The thickness of the board.

2. How much a screw has to go into the fin for the threads to start grabbing.

3. How far you can put the screw in the fin before it bottoms out.

So,

1. With the fin off the board, put the screw in the fin until it first grabs.

2. Carefully count the number of complete turns of the screw it will take before the screw bottoms out. This is very important to keep from stripping the threads in the fin. The hole for the fin is only so deep. If you keep cranking on the screw after it has bottomed out in the hole, you will strip the threads in the fin.

3. Now that you know the maximum number of complete turns for that fin, take the screw out of the fin. Put the fin in the board, and put the fin screw in until it first grabs.

4. Count the number of turns until the fin is tight in the box, but don't exceed that maximum number. If you get to the maximum turns, and it still isn't tight, you can either get a shorter screw, or add some washers on the top deck of the board.

5. I've gone out with as few as 3 full turns, but 4 or 5 or more is better

beallmd · Joined: 10 May 1998 Posts: 984

If you look around the hardware stores eventually you can find european stainless screws that are correct. Most of the shops keep a good supply. I keep a few of different lengths. I had one screw that would "bottom out", so that while screwed all the way down the fin was loose in the box. I added 2 stainless steel washers that were part of the permanent set up.
Quick story; We were at the shop in Maui and wanted to replace a fin on a rental board. We took the fin screw out, being used to Powerboxes, but the fin was "stuck." So with the shop employee we got a rubber hammer (almost as handy as duct tape) and started pounding away. One of the other-okay, smarter-employees ran out and said stop. Turns out it was a Tuttle and had a second screw that was still in and was hidden under the footstrap. OOPS!

scargo · Joined: 19 May 2007 Posts: 235

KonaJoe's method is fine, but why not make life easier. Just by looking at your powerbox fin, you can tell where the brass nut is in relation to the bottom of the board. So just put a stick (a skewer or long matchstick works well), and mark it with a marker. Then cut off your screw and file the threads with a fine file. I lost a fin once, and have taken to using a lock washer on top of a regular flat washer. And for a really nice fit you can sandwich in a rubber washer between two flat washer. Obviously, you have to factor all of that in before cutting the screw.

dsgrntlxmply · Joined: 16 Jun 2010 Posts: 180

Some of these screws can be bizarre sizes: mine (Powerbox on an RRD Fireride twin-fin) is an M6 x 1.0 x 52mm.

It is difficult to find an M6 longer than 40mm in stainless. Even if a 55mm or 60mm length can be located, it will still need to be cut down.

bsangeor · Joined: 11 Jun 2005 Posts: 96 Location: SE Michigan

ColdWater · Joined: 04 Mar 2012 Posts: 12