Is this a Mk5 bolt

[uhjohnson]

Is this slot a feature of a Mk5 No1 bolt

[browningautorifle]

We need a pic for this one.

[uhjohnson]

Was the long slot in the bolt lug an identifying feature of a No5 Mk1

[browningautorifle]

No, the hollow bolt knob...

[Alan de Enfield]

No, the hollow bolt knob...

But some No4's had hollow bolt knobs as a variation of manufacture - it was used as a 'location' point for tooling.
The trick is to recognise which 'hole' is which'

[Alan de Enfield]

Is this slot a feature of a Mk5 No1 bolt

If this is the same bolt that you have posted about on other forums, NO, the slot was a No4 bolt which carried over onto the No5.
To all intents and purposes the No4 and No5 bolts are identical except for the enlarged 'hole' in the handle (supposedly to save a few fractions of an ounce in weight)

[browningautorifle]

The trick is to recognize which 'hole' is which'

That's true.

[browningautorifle]

the enlarged 'hole' in the handle

That's the one...

[Surpmil]

The long slot in the long recoil lug is standard to all No4 and No5 rifles and originates in the No1 MkVI if I remember correctly.

As for the bolt knob hole, some No5s had a considerably larger hole than the No4s, and the knob was also shortened somewhat. The hole sizes were about 3/8" versus 1/2" as I recall.

I doubt the hole was ever used for work-holding during manufacture, if only because plenty of other bolts (No1 No4) were made with no hole at all)

[Alan de Enfield]

I doubt the hole was ever used for work-holding during manufacture, if only because plenty of other bolts (No1 No4) were made with no hole at all)

When I mentioned that, it was as a result of coming across an old PL post where he states that one (No4) manufacturer requested a deviation to the original specification (no-hole) to allow ease of 'jigging-up'.