Indigo Dreaming

The journeys of the Narrowboat Indigo Dream

  • Blog Index as a pull down

  • Recent Posts

  • Meta

  • Recent Comments

  • wordpress counter

Technical Stuff: Locking Fuel Caps and Arcane Measurements

Posted by indigodream on 9 August, 2008

While Sue rambles on in the Odyssey I thought you’d be interested in some technical man-type stuff…..

Last week I described my deliberations about fitting a locking cap to our diesel tank. I settled for a locking cap from Fuelock – a company run by a guy who currently is on his yachty thing somewhere in a marina near Glasgow.

The cap duly came by mail order so on Friday the first job was to install it. The cap is nicely made in a rigid plastic with an offset cam lock. I didn’t want an armour plated cap, so this looked perfect or so I thought.

Just one minor problem: We needed a cap which was 1½” (38mm) across threads, the Fuelock is marketed as a 1½” BSP fitting so seemed perfect. What we did not realise is that a 1½” BSP fitting actually measures 1.882″ (47.803mm) so the ‘fitting’ did not fit!

Where on earth do these odd measurements come from? How can 1.5″ = 1.882″. Oops, our mistake, we have now looked it up so now know that it is about the internal diameter of the pipe with that thread on the outside measured in furlongs multiplied by 7920. Straight forward and obvious.

So if you have a filler cap which measures just over 1¾” then seriously consider getting a Fuelock. If it’s any other variant of 1.5″ then get something else.

Confusingly looking at, say, the aquafax web site then deck fillers are either 1½” or 2″. Next time we get into a Chandlery we will measure all the fittings we can get hold of. Is ours odd or are narrowboat fittings generally different to what gets fitted to Yachts? If our fitting is odd then we need to look if we can simply change out fitting to a larger one – we just need a few mm, could there be that much play in the steel?

Richard talked to Fuelock. They have a straightforward money back guarantee – if it does not fit then send it back and they give you a refund. No quibble, really nice people to deal with. The guy at Fuelock is trying to work out whether its worth making them in different sizes but is himself a bit confused by what narrowboats have for fillers ….

2 Responses to “Technical Stuff: Locking Fuel Caps and Arcane Measurements”

  1. Dear Indigo Dream

    We now have a fuelock that should fit your 1 1/4 bsp fuel filler. It works on the same method as its big brother so if you are still interested please visit

    best regards

  2. indigodream said

    Hi Kevin

    I’m sorry but you are too late! 🙂


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: