Record vice jaw screw - tap size

[Haz87]

Long story short, both screws that held one of the jaws on my (Irwin) record sheared flush. I've managed to get one remain out but the other is stuck solid.
I need to work out how to get the vice apart so I can get a drill at it properly first but does anyone know what tap size I'll need to sort this?
I believe it's 5/16" but I'm seeing all these different tpis listed when looking. Is 18 right?

Cheers,
Harry

 

[Pete.]

That's gonna be 5/16" BSW (Whitworth) IMO.

 

[Agroshield]

Pending a definitive answer from someone who knows, take a photo of the bit you pulled out next to a ruler. Actually take two photos, one on the imperial side and one on the metric side. As close up as possible and as straight above as possible. Then it should be possible to identify the pitch.

If there is no doubt that it is imperial (i.e. no Irwin vise has yet been made with metric threads), then 18tpi is correct for a 5/16 coarse thread in both Whitworth and UN. The photo will allow easy determination of coarse or fine.

 

[Moose McAlpine]

On my Record 25 they're ¼-20 UNC

 

[500e]

And the jaws are Hard

 

[Haz87]

Right, first pic is the original screw (well one from the other jaw that I didn't feck up!)


Based on googling, everyone said 5/16 x 1", so I ordered that as it was worth a punt for a fiver, and what has arrived is huuuge



I'm a metric guy, so I'm just peeing in the wind at this point. Don't really fancy keep spending out on random (wrong) screws tho so any help muchos appreciated here!

 

[Haz87]

Its only after taking the pics, that they obviously aren't 1" in length, even I've worked out that bit. Its just the rest I'm not qualified to suss

 

[123hotchef]

mine are M6 now or wait are they M8

 

[Moose McAlpine]

Do you have a thread gauge?

What vice is it?