Thread: Strange thread question

I have an old 20L red plastic outboard motor fuel tank that I want to adapt to act as a water/coolant tank for the wood bandsaw mill.
It looks like this
Screen Shot 2021-12-12 at 5.41.27 pm.png


Currently the mill is hooked up to a tap via a couple of 30m long hoses that have about 5 joins. The closest tap is on the other side of a drive way where trucks constantly pass over the hose. As a result hose leaks and water pisses out everywhere making a muddy drive way and soggy sawdust walking paths. Rolling the out out and back every time I mill is also a major PITA.

What I want to do is set up a 20L reservoir on the new mill where I can mix water and a shot of dishwashing liquid and just dribble enough onto the blade to provide the necessary band cooling/lube. Our new mill has this arrangement and it works really well. It uses far less water and as a result leaves far less mess.

Th fuel tank has a standard black fill cap and a valved outlet which I have removed and want to replace with a threaded gland to hold a length of hose deep down inside the tank to reach the bottom of the tank when its standing upright.

The brass thread on the valved outlet is about 16.5 - 16.6 mm OD and the closest match I can get is about 18TPI. Anyone know what this might be.

Before anyone has an OHS fit - the tank will be clearly marked just in case any eedjet wants to steal it for whatever reason.

3/8 NPT would be pretty close.

18TPI in that size is also very close to both M16 x1.5 conduit thread, and 5/8 UNF
I’d probably suggest it’s more likely NPT though. BSP in that size is 19TPI

Are you sure it is 18TPI?

Thanks Everyone.
A 3/8 NPT nipple screws into it so I guess that is what it is.
I don't know why I didn't try that earlier.

A 16mm cable gland should screw in no problems. The plastic is soft enough to mould itself to the thread. A lot of the gear I used to work on was american so most cable threads were npt and metric glands screw in easily.

Before anyone has an OHS fit - the tank will be clearly marked just in case any eedjet wants to steal it for whatever reason.
Why should this worry you?
Think of it as a contribution to Darwin.

Cheers
Roger

Nothing particularly Darwinian about 20L of dishwashing water

RE: Safety.
The sawmill sits outside with most off the upright frame and Kohler motor covered by a roped down large tarp.
It already has a 20L outboard fuel tank sitting flat in a frame also under the tarp.
The water tank will sit alongside the fuel tank.
If someone does remove the tarp and wants to steal a tank - my guess is they will see WATER written on the side of the water tank and will steal the real fuel tank.

Originally Posted by BobL

RE: Safety.
The sawmill sits outside with most off the upright frame and Kohler motor covered by a roped down large tarp.
It already has a 20L outboard fuel tank sitting flat in a frame also under the tarp.
The water tank will sit alongside the fuel tank.
If someone does remove the tarp and wants to steal a tank - my guess is they will see WATER written on the side of the water tank and will steal the real fuel tank.

You really expect anyone stealing it will be able to, or take the trouble to read what has been written on the tank

Originally Posted by droog

You really expect anyone stealing it will be able to, or take the trouble to read what has been written on the tank

Not really. The tank is also pretty beat up which I think is why it was retired as a boat fuel tank. I anything they will steal teh fuel tank.

I would have piped up sooner being an outboard mechanic had I seen this thread earlier. The threaded fuel tank fittings are all generally NPT so most of and if not all the outboard fuel tanks are threaded NPT. Just some info for those that don't know NPT and BSP fittings will go together as they are only thread pitch different, but they can be tight but they will go together.