Seat Bolt Question for my '91 Roberts

[Thame Game]

The last part to fit and I'm not sure what fits?
The outside frame length is 23mm
Inside frame is 15mm
Bolt diameter is 6mm

It's notched as well. Anyone know or have what Roberts were using in the period?

 

[gtturbo]

Something like this I would have thought ?. Although this might not necessary be the right size.

https://www.sjscycles.co.uk/seat-posts/vintage-style-steel-seat-post-binder-bolt-16mm/

 

[Thame Game]

Something like this I would have thought ?. Although this might not necessary be the right size.

https://www.sjscycles.co.uk/seat-posts/vintage-style-steel-seat-post-binder-bolt-16mm/

Yes, I've looked at similar on ebay, but that 8mm shank is too long for the notch to engage with the frame.

 

[Mark Manley]

Is it not just a standard M6 allen screw? My '94 Roughstuff is.

Just noticed that you have a 6mm through hole, should there be a thread in there that has stripped?

 

[Thame Game]

Is it not just a standard M6 allen screw? My '94 Roughstuff is.

Just noticed that you have a 6mm through hole, should there be a thread in there that has stripped?

It's a strange one. No signs of there ever being a thread in there. Clean as a whistle (sorry, all the white gunk is t-cut).
You're right about it being 6mm right through. Both sides are countersunk as well, as if to take countersunk washers?

 

[Thame Game]

I'm now thinking its designed for a quick-release. They are m6 with gubbins to sit in the frame.