Unidentified Thread in Bathroom Fitting

[TheScullster]

Hi all

My mother collared me the other day with a request to fix a toilet roll holder. At first I couldn't see anything wrong, but eventually found that a grubscrew is missing. This grubscrew centralises a chrome flap which half covers the toilet roll and, I think, provides the user with a flat edge to tear the serated sheets off against IYSWIM. The strange thing is, the thread does not conform to UNC, UNF or metric pitching. Fortunately, the grubscrew that retains the holder onto its wall bracket is the same thread, so this can be examined closely.

Are these fittings renowned for using odd-ball thread types? The toilet roll holder was part of a refurb job, so unfortunately maker's details are not known.

TIA

Phil

[newshound]

Not an uncommon problem. Does it have to be a grub screw? Is it into an alloy casting, or steel? For alloy, I'd probably be looking in my box of assorted self tappers. Unless it's very fancy or there's a quick fix you're probably better to thow it away.

>

[Dave Plowman (News)]

[Matty F]

What is the approximate diameter?

[The Natural Philosopher]

Probably BSP thn..

[Matty F]

When I was sorting out a ton of old bolts I made up a table so that I could work out what they were. It's too big to post all of it as it covers 1/16 inch to 6 inch diameter threads. But it has only BA BSF BSW M MF UNC UNEF UNF as I don't use pipes :)

[TheScullster]

"Matty F" wrote

Took the fitting to the town's iron mongers on saturday. Using a drill gauge type-thing, the guy reckoned it was 5/32" dia. The only nut that would come anywhere near it was M4, but an M4 screw would not fit into the threaded hole. Also when visually comparing the threads, metric wasn't close, nor were UNC, UNF, or BA (all of these were finer than the grub screw). Looks like it will have to be drilled and tapped out to a suitable "standard" size :(.

Phil

[Matty F]

Here's part of the table, sorted in diameter order:

Type Size Dia Inch TPI Dia mm Pitch mm BSW 1/16 0.0625 60 1.59 0.42 M 1.6 0.063 72.57 1.6 0.35 M 2 0.079 63.50 2 0.4 BSW 3/32 0.09375 48 2.38 0.53 M 2.5 0.098 56.44 2.5 0.45 MF 3 0.118 72.57 3 0.35 M 3 0.118 50.80 3 0.5 BSW 1/8 0.125 40 3.18 0.64 M 3.5 0.138 42.33 3.5 0.6 BSW 5/32 0.15625 32 3.97 0.79 MF 4 0.157 50.80 4 0.5 M 4 0.157 36.29 4 0.7 BA 3 0.1614 34.84 4.10 0.73 M 4.5 0.177 33.87 4.5 0.75 BA 2 0.185 31.35 4.70 0.81 BSF 3/16 0.1875 32 4.76 0.79 BSW 3/16 0.1875 24 4.76 1.06 MF 5 0.197 50.80 5 0.5 M 5 0.197 31.75 5 0.8

[Dave Plowman (News)]

Only common coarse thread you've missed out is Whitworth.

[Andy Dingley]

Remember that metric has both fine and coarse pitch. For most sizes the coarse variant is pretty rare, but they might have used it in castings?

I'd be looking at the next larger self-tapper I had handy, ideally a Taptite (slightly different thread profile) as the least-abusive way to bludgeon a thread into a cheap diecasting.