Backnut size

[Jeff Layman]

What is the standard size for a backnut across its flats?

I was trying to undo a plastic backnut holding a 3-year old tap onto the basin in the bathroom but the smaller of the basin wrench ends was too small, and the other much too big. The smaller measured 15/16" (c24 mm I think) across the flats. I can't get to the plastic backnut to measure it, but I would guess it's around 1" across the flats, and seems a couple of mm wider across its flats than the brass nut holding the water pipe to the tap. Apologies for the imperial/metric sizes, but I hope you get the idea.

As far as I can tell, fixed-size basin wrenches are meant to undo nuts for 15mm and 22mm pipe. Are they meant to be used to undo the backnut I referred to, or is something else required?

Of course, none of this helped by the awkward position to work in, and the 5 - 10mm indentation where the backnut tightens on the underside of the sink which limits the positioning of the wrench.

[alan_m]

I've found the same with basin spanners and I have two which are slightly different sizes across the flats by a mm or so - down it poor manufacturing tolerances. For back nuts I use box spanners but I need to remove the connecting pipe/flexi first. To get a greater reach box spanners can be stacked - a smaller box spanner will fit in to the end of a slightly larger box spanner. On a sloppy fit a box spanner will still grip on six points around the back-nut. I now always replace plastic back nuts with brass and select ones with some depth. Some of the plastic ones I've encountered have been so thin that getting any spanner on them would be difficult.

[Dave Plowman (News]

Par for the course with many plumbing fittings. Makers seem to make their own mind up what AF the nuts will be. Perhaps owned by Apple?

[John Rumm]

Alas there is no real standard. Even compression fitting backnuts had an amount of variance. Hence adjustable wrenches of various types featuring heavily in a plumbing toolkit.

Ad adjustable basin wrench may be your friend here.

Yup - many designed by someone who has never had to fasten something to one I expect!

[Andy Burns]

If apple did plumbing, you'd need some funky 7-sided spanner, and they'd refuse to sell spare washers.

[Jeff Layman]

Thanks for all the replies. It's good to know that it's not just me!

I'd looked at adjustable wrenches but they seemed to get varying reviews. It doesn't look like there is an alternative, though, so I'll have to get one next week.

[Animal]

If you can't fit an adjustable in there, or don't have one, you can always tape some coins to the inner edge of the too big spanner end. Sometimes they even stay in place while you undo the nut. Usually, plastic tap nuts undo themselves on the day of fitting.

[newshound]

You can't put too much torque on plastic nuts. I usually use a "water pump spanner" but (on waste fittings) have sometimes used a strap wrench, or one of those spiky kitchen things used for removing jam jar caps.

[Dave Plowman (News]

Being old, I have car spanners of about that size. In Whitworth, AF and metric. Can usually find one that's a good fit.

[Jeff Layman]

Possibly, but surely the ends aren't at 90° to the shaft. Or have you taken a club hammer to them?! I thought I had an old bicycle spanner which might fit, but I couldn't find it.

I think I'll stick 1 mm or so wide plastic or aluminium shims to the wider end jaws of the basin wrench until it just fits the plastic nut. If not, as Animal suggest, I'll try some coins. I'm sure I've got some of those little 5p pieces which seem to get lost regularly, and for which I have little purpose now just about everything's pay by card.

[Brian Gaff (Sofa]

Apple have rather had a turn around recently,with some of their newer phones but that aside, I do remember a battery lawn mower I had with completely weird bolt heads, and nuts, and indeed who remembers those TVs with security screws that only bona fide dealers were allowed to have. Brian