I'd guess glass is the best bet.. depends how big the window is but watch glasses come is huge range of sizes example to 38.3mm here: **LINK**

pgk

I was going to suggest watch crystal glass. It's available in a complete myriad of sizes. usually the sizing is described as 383 for 38.3 as described by pgk pgk above.

Certain filling station near Manchester had a metal dipstick which was ever so slightly too long so it rested on the bottom of the tank. Over the years repeated impact of dipstick on tank floor caused a hole in the tank How expensive did that prove, not only a tank full of petrol but a huge clean up bill.

Yes, but…..

Volumetric expansion is the linear vaue to the power of three, so far more significant than linear expasion. (Double one dimension and volume doubles, but double all three dimensions and the volume increases by a factor of eight).

Remember, too, that the tank could be expanding with temperature rise as well. Dips, I woud think, were more important as a backup before electronic metering was fully deveoped. Should only be needed to avoid over-filling storage tanks these days (or running empty, of course).

My 30 + year old Stiga mower has a plastic cover for the fuel gauge / dip stick and that fell to bit's years ago…..

I now use an old bean tin as a water proof cover…….the gauge still works and for those that need to know the gauge needle is opertated by a float sliding up and down on a twisted metal strip……

the mower will out last me and if the can rots there's plenty more in the cupboard…….hahaha……

have fun on ya mower

Fascinating how you claim that "wood was never allowed" when I used a set of wooden dips every day every summer for years while working at my grandfather's service station and later on diesel tanks at a truck stop. Last week I saw a set of wood dips on a rack next to tanks at a busy gas station just east of where I live.

At the old garage and the truck stop we saw far more differences in fuel levels due to water in the tanks (water would be regularly removed) and evaporation in hot weather than from material of the dip sticks. In "condensing" weather (hot days cool nights) there could be two inches of water form in the larger tanks overnight.

Dip technique (straight up and down vs angled entry to the tank) could also make a significant distance in measured levels.

None of these variables affected amounts dispensed accurately to the consumer – that was controlled by the pumps. The tank levels were monitored mostly for knowing when to re-order fuel from the oil company. Tank lids were padlocked , were heavy castings, and checked at start and end of every day to deter theft.

Course that didn't keep idiots from trying to steal gas. Regularly we would arrive at the station in the morning and find someone had cut a hose between pump and nozzle to try to get gas, or had broken the padlock on the pump on/off lever to try and get gas (or both were done). Never worked because the feed valves and electrical supply to the pumps were inside the garage and were always shut off before we left.

Petrol affects wood.

Years ago my Marina got written off. I cut the fuel hose and filled a petrol tank, plugging the hose with a pencil. I forgot about it for a few weeks, when I pulled the pencil out for a refill it was as bendy as rubber.

Neil, I have no doubt that petrol / gasoline will have major effects on wood if left immersed. For dips they are only in and out of the fuel for a few seconds at a time. Never seen a wood one break down from fuel exposure, but they might if left immersed.

Mike Poole- polycarbonate used to be OK for petrol / gasoline exposure but I have seen some PC parts degrade quickly in modern fuels. I think it may be caused by some of the nastier fuel additives being used now. Some time ago in industry I had to ask around resin manufacturers for a transparent plastic recommendation for the housing of an opto-electronic fuel level sensor. Couldn't find a manufacturer or resin that is rated / certified not to crack craze or become opaque for one or two years while exposed to modern fuel or fuel vapour. There may be one, but I couldn't find it.

Is the existing clear part flat or top-hat shaped? Most of the ones I've seen on small engines are top hat shaped or have curved flanges, and were moulded plastic originally (not sure which plastic though.)

If flat, a watch crystal could certainly work. Most glass shops in my area that do cutting of glass can cut a round flat piece to order. I've had some done for lamp restorations. Ones local to you may also be able to cut rounds.

That's why I suggested the wood stick fuel gauge for Mark's mower tank originally. Can't beat the price, and the risks are mighty low.The bean can cover idea that Clogs suggested is also a very simple and cost effective alternative to finding a suitable plastic or glass bit that will do the job.

You might try a look at the Stens website in the USA, they make or distribute a huge variety of small engine parts. They may have a replacement fuel gauge assy of the type you need. Example below.

Edited By Jeff Dayman on 03/06/2018 21:35:24