correct size allen key for tightening square recessed valve

[einhorn]

we have a central heating system which is 15-20 years old. At the end of the pipework feeding many of the radiators is a partially recessed square nut below which is a spout which I guess is for bleeding the pipework. Some of these square nuts periodically work loose and need to be tightened. And here the problem starts. I have a heavy bronze type allen key which I think came with the central heating system in the shape of a triangle and at each end a different sized allen key marked, 1, 3/4 and 1/2 respectively. I am not sure what these figures refer to as the actual size of the square nut is 7 mm square. I have used this allen key in the past with great difficulty to tighten up some of the nuts as the bulky triangular shape makes locating it square over the nut virtually impossible as it fouls up with the wall and pipework which are very close and restrict access. What I need is just 1 allen key of the right size which will allow access in a restricted space. In the past after much faffing I used either the 3/4 or 1/2 size on the triangle but am mystified how this relates to the 7 mm square nut sizewise.
Would be very grateful for any help and what to ask for. Also can anyone recommend good internet companies who sell this type of product.
Many thanks, Regards, Frank.

 

[swbjackson]

What you have is an Isle of Mann key which is not designed to operate the drain offs that you are trying to tighten. A radiator bleed key normally fits these valves.

 

[JohnD]

show us a picture

//www.diynot.com/forums/viewtopic.php?t=129539

I wonder if you mean
http://www.screwfix.com/p/angled-radiator-valve-drain-off-15mm-x/70408
or
http://www.screwfix.com/p/drain-cock-type-a-heavy-pattern/96725

 

[einhorn]

Thanks John D, afraid never got to learn how to add pics, will have to remedy.

Your picture enclosure Drain Cock Type A Heavy Pattern is very similar to our set up. The drain cock is fitted to the end of the pipe run quite seperate and below and to one side of the radiator. The 4 sided nut is partially sleeved so difficult to gain purchase with anything other than correct sized "key" and very close to wall/pipework making manouvering awkward. The 4 sided nut, similar to radiator bleed valve, measures 7 mm diameter.

Appreciate your thoughts please.

All the best, Frank.

 

[JohnD]

I do mine with a Brake Bleeding Nipple spanner from Halfords.
I think it has one 1/4" end and one 3/8" end

You could try a small socket set as sold with a screwdriver-type handle. They usually come with a square adaptor that might be 1/4" and enough metric sockets that one will fit, though I don't know about this sleeving you mention.

The rubber washers in those drain cocks usually need to be replaced after use.

http://www.screwfix.com/p/forge-steel-64pc-ratchet-screwdriver-socket-set/78939?_requestid=759119 very cheap

they usually come with an adaptor/extension bar that I can't see in that kit.