Red Fibre 'Pre-Threaded' Tight Fit 1/4" BSP Washers (i.e. Sump Plugs/Unions) - Pack of 5

Product no.: 0249 A11/719FW

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These Red Fibre Washers are a smaller diameter than 'normal' 1/4" BSP washers - but then pre-threaded by us - so they are a good fit on those Norton fittings that used 1/4" BSP thread, but have a groove behind the thread - e.g. Norton pre-48 Oil Sump Plugs and some breather union fittings. 

This listing is for a bag of 5 washers


For anyone that is familiar with Norton single cylinder models (and earlier twins) - they will know that it was not unusual to make some oil and petrol fittings with a 1/4"BSP thread, but with a groove machined between the thread and the rear face of hex spanner head.  Added this, often the hex was not very wide (what you will see referred to as 'Reduced Hex' by us throughout this catalog for Norton specific fastenings), so there was little hex face for the fibre washers to seal against.  

The two best examples of this are the Pre-48 style 1/4" BSP Norton Sump Plug (in all its guises) and some breather unions (see photographs - some Unions had grooves, while others did not).

Therefore, if you try and fit a 'normal' 1/4" BSP red fibre washer to this type of sump plug or union - it will go on easily, but when it gets to the groove - it will wobble around.  Then, when the sump plug or union it tightened, the wobbling washer will normally move over to one side - and there will be a very good chance it will leak, or just crush and break up when tightened.

In the past we have sold this size of 'tighter fit' washer - telling customers they will need to be prepared to use some force to wind the washer past the thread - but franky - the best quality red fibre washers are very hard, and extremely difficult to wind onto the thread!

Therefore, as part of work we did in early 2022 to replicate most Norton sump plugs, we also looked at how we could make this easier - and eventually have come up with a jig process to pre-thread these washers with a 1/4" BSP thread - as shown here.

So, although not very thick - if you look closely at these washers you will see they have an intenal thread cut into them (see also the taper tap we use for this process) . . . and that means that, although still tight, they can now be carefully screwed onto a 1/4" BSP thread by hand - but will a 'Size' fit on the groove behind the thread - therefore giving a much better chance for the washer to seal properly!

If trying to tap a single washer, it will normally just crush the washer, but with experimentation and a jig, we have come up with a process to manualy thread these washers, so they will just 'screw on' by hand.

This may sound like a simple issue . . . but actually most proprietary 1/4" BSP washers are actually quite loose on a 1/4" BSP thread (see our Item 1111 for 1/4" BSP washers that are a good fit!), but good quality red fibre washers are normally much harder than cheap washers - the washers we use are supplied by one of the best (and most expensive!) washer suppliers - and therefore require this pre-threading process . .. trying to screw it on without doing this is almost impossible.

Sorry these washers are so expensive for what looks such a simple and cheap looking thing - but hopefully you will understand that the jig and time it takes to manually thread them is what results in the extra cost - but definitely worth using if you prefer the original type Red Fibre washerer, rather than modern Dowty (nitrile/steel) washers.

We also sell these as a pair (Item 0941), or close fitting 'normal' 1/4" BSP washers (Item 1111) for those unions and tap fittings which dont have a groove behind the thread 


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