Red Fibre Washers: Fibre Washers, as originally fitted behind all Norton SOHC, OHV and sidevalve engine cover cheesehead screws.
These look to have been original fitment behind the cheesehead screws used on crankcase timing covers (all single cylinder models), cambox covers (SOHC) and rockerbox covers (OHV) from the late 1920's - late 1950's.
They act as a buffer behind the head of the cheesehead screw and the aluminium timing cover and give a better, more even purchase on the cover/casting. You may find if you are restoring an engine - sometimes the old fibre washer is perished still in place - in which case it can be easily removed with a scriber or similar - or may not have been refitted if originally lost. Regardless - I would recommend you do fit them, on all timing covers and cambox/rockerbox covers, as they help protect the casting and allow a better purchase.
Interestingly - most Norton gearbox's I have stripped do not seem to have used red fibre washers behind the cheesehead screws - and they are not listed on most Spare Parts catalogs. Therefore, as standard - all our 'engine' cheesehead screw sets come complete with these red fibre washers in the set, but the gearbox cheesehead sets do not. However, there is no reason you should not fit these to your gearbox screws if you wish - I sometimes do!
These particular washers are premium quality (quite hard) from a top manufacturer, so are durable and long lasting - and explains why the price may seem higher than expected - but they are far more durable than other similar washers you may find available commercially - I would never use any other type.