Die cast box screws type?

[stevehertz]

I have a diecast box from the 80s where a couple of the mounting screws were troublesome to undo, I ended up drilling the heads off then undoing the remaining threaded parts using a pair of pliers. I thought that they would be 4BA but that's slightly too big, and they're not - as far as I can see - metric either. Any ideas what type and size they might be? Thanks.

[Cruisin Marine]

https://www.canford.co.uk/EDDYSTONE-DIECAST-BOXES

[Panrock]

As per the last post, I've always assumed they're M3.5, Steve. Maybe the fact they're 'taptite' means they feel stiffer to rotate though?

Steve

[Phil__G]

I'm forever losing Eddystone screws so I bought a bag from RS. They're M3.5 or at least mine were:
https://uk.rs-online.com/web/p/machine-screws/9087491/

Since found some genuine ones here:
https://www.canford.co.uk/Products/1...OX-Spare-screw

[stevehertz]

Thanks guys. I only tried M3 and M4 (which I stock) so 3.5 would make sense.

[Philips210]

Originally Posted by stevehertz

Thanks guys. I only tried M3 and M4 (which I stock) so 3.5 would make sense.

Electrical fittings such as 13A wall sockets and light switches use M3.5 screws for fixing to the pattress etc so may be useful as a test to confirm.

Regards,
Symon

[emeritus]

The cover screws of the Eddystone die cast boxes we were using in the early 1970's were M3.5

[barrymagrec]

In my experience very old die cast boxes were 4BA but a long time ago they changed to M3.5, about the same time as electrical fitting wall boxes (switches and sockets) did the same.

[Simondm]

Originally Posted by barrymagrec

In my experience very old die cast boxes were 4BA but a long time ago they changed to M3.5, about the same time as electrical fitting wall boxes (switches and sockets) did the same.

Wot 'ee said.

M3.5 and 4BA are annoyingly close. I've been caught out by old Eddy boxes many times in the past.

M3.5 is, of course "second series", meaning that cheaper sets of taps and dies don't have that size included. You can get the tap fairly easily from electrical factors (often fitted into a plastic handle), but I don't think I've ever set eyes on a 3.5 die.

I wouldn't be tempted to run a tap into an Eddy box though, unless I knew for certain which it was supposed to be.

And just to put a tin lid on it, I'm pretty certain that the die-cast boxes Maplin sold at the end of their run had 3mm threads (but they're easy to spot as they look suspiciously weedy).

[TonyDuell]

6-32 UNC is also a somewhat similar size.

UK electrical switches/sockets changed, as others have said, from 4BA to M3.5

HPIB cable jackscrews were originally 6-32 UNC (and a nickel-plated finish) and changed to M3.5 (black oxide finish)

I have the set of 3 M3.5 taps (taper, second cut, plug) to use with a tap wrench. I can't remember if I have the die, but a good engineering tool supplier should be able to get it.

[barrymagrec]

Originally Posted by TonyDuell

6-32 UNC is also a somewhat similar size.



HPIB cable jackscrews were originally 6-32 UNC (and a nickel-plated finish) and changed to M3.5 (black oxide finish)

I

HPIB was 6-32 but the similar but not quite identical later IEE488 was metric, if I remember correctly.

[davidw]

When faced similar problems I just use a self tapping screw of appropriate size. I know its a bodge but it works.

[Herald1360]

Less crude but effective (especially if the original hole threads are tired)- tap out to M4!

You might need a touch of countersink if you need flush fitting screwheads.

[John Caswell]

I think you will find that are 3.5 mm trilobular taptite screws. The ones in my boxes are.

John