SJS probably
https://www.sjscycles.co.uk/seat-posts/seat-bolt-traditional-nut-bolt-type-1-34-inch/
Brilliant - Thanks.
Turns out that I have a few similarish in my odds & sods bolt box from an old dalliance with rebuilding 50s bike up.
@NotThamesWater started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
SJS probably
https://www.sjscycles.co.uk/seat-posts/seat-bolt-traditional-nut-bolt-type-1-34-inch/