Need help finding specific pin screw

[royc75]

Hello

Hope I'm in the right place.
In my bath there is a tap that's connected using a pin, that pin is missing and I'm not sure what's it called or what to search for online.
It looks like a very small octagon shaped pin, probably around few cm long that can be screwed in using proper hex key. I've attached photos which I hope would help someone resolve that mystery for me

Untitled

• royc75
• 30 Jul 2013
• 1

Untitled

• royc75
• 30 Jul 2013
• 1

Thanks!

 

[Burnerman]

It a bit difficult to see, but it looks like an ordinary hexagon allen grub screw (screw without a head).
I don't get the octagonal bit though?
John

 

[royc75]

Thanks, sorry meant hexagon

Looking on images on eBay I think you are right that's the one I need but how can I tell the diameter I need it is very hard to measure...

 

[Dave54]

If you haven't got a calliper of some type to measure it, then compare it to the shank of a (metric) ordinary twist drill. The thread will be very slightly smaller than the "right" drill. (ETA ignore this bit, it was me assuming you had a grub screw. I need to engage brain before operating keyboard!)
At a guess it'll be M3 M4 or M5.
Looking in the thread tables it also appears that a drill 1mm smaller will fit into the tapped hole at those sizes. In other words a 2mm drill will fit into a M3 tapped hole, 3mm into M4, although if it's M5 it may be a bit tight with a 4mm drill. I haven't tried this though!

 

[royc75]

Thanks Dave.

So, I just bought this hex set on eBay: http://www.ebay.co.uk/itm/231001358991?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

I will see which drill fits and then buy one size bigger!

 

[Dave54]

It only works with those sizes I've given. (or should do according to the table I have) M6 for example will not take a 5mm drill, but will be a very slack 4mm. Good luck with it.
ETA Just tried this in the workshop for interest's sake. It appears that a 6mm nut takes a 5 mm drill shank snugly. The figures in the tables don't take manufacturing tolerances into account of course.

 

[royc75]

Ok so I got the hex set and I can fit the 3mm in (4 is too big already).
Given the responses above I'm assuming I need M4 but when.I search online some say that 3mm key actually works with M5 not M4...

Any ideas?

 

[Burnerman]

Are we talking about the thread size here, or the allen key size that fits into the hexagon?
A 3mm allen key refers to the 'across flats' dimension of the key.....and half sizes are sometimes used!
John

 

[royc75]

We are talking about the hex key size that fits into the hole, I havn't bought the grab screws yet as unsure on the size (M4 or M5)...

Thanks

 

[royc75]

Correction: I just unscrewed the other tap that has the exact same hex screw using 2.5mm hex key. So, I suppose I need the M3 one as these don't come in half sizes right?

 

[royc75]

And on this eBay item it says that M5 fits 2.5mm Allen key:
http://bit.ly/15lr5mf

I'm confused!

 

[Burnerman]

As a general rule, and these need not be specific - a 2mm allen key fits a 4mm grub screw, and a 2.5mm allen key fits a 5mm grub screw.
John

 

[royc75]

M5 it is then