What size Allen key required for Rad Valve extensions?

[The Night Tripper]

I recently bought a (Fixed, 20mm) Rad valve extension for the first time. I saw that it required an allen key for fitting and assumed that my standard Radiator Key would fit. Not so, to my surprise and also that of the plumbers merchant I bought th extension from.

It looks like it need an Allen key of around 11.5mm AF. Is there an imperial equivalent size, and where do I get a key to fit please?

Thanks Jon N

[Bob Minchin]

7/16 is 11.1mm

The other way is a flat steel strip filed to fit across opposite corners of the hexagon.

Bob

[cynic]

There is a pukka tool to do the job it has a tapered hexagon at one end and a square with a recess at the other with a tommy bar in the middle. I think Monument make them and sell through Wolsely Centres plus other outlets.

[The Night Tripper]

Hi there thanks for the replies. I've now seen the Monument tool (search for "universal radiator key".

I might measure the size properly (when I find my vernier) and buy a corresponding imperial Allen Key, if that's what it turns out to be - there are plenty on eBay. I recently inherited my late Father's extensive tool collection, including boxes and boxes of Allen keys, but surprisingly don't seem to have one to fit.

Regards Jon N

[John Rumm]

The proper keys also usually have an end to deal with those that have a square section rather than hex.

[The Night Tripper]

yes, my 'non-universal but standard' key has one of those. It was that key which doesn't fit, to my initial surprise.

I've measured the size as a 'just a whisker under 12mm' AF. My 12mm Socket head just doesn't fit. Bob minchin's suggestion of 7/16" sounds like it might be a bit small, but probably worth trying. I'm still surprised they make these adapters with such an unusual size hole...

Thanks Jon N