What the 13.3 mm? Seat post bolt on old British built Raleigh.

[uart]

I was taking the seat post out of an old Raleigh today (British built) and my 13mm spanner definitely wouldn't fit - but my 14mm was a loose as can be. Anyway I removed it with a shifter and it measures almost exactly 13.3 mm (no corrosion or burrs or anything btw, totally clean).

So what is it, 17/32 inch I guess? Well that's closer to 13.5 mm but it's not uncommon for bolts to be a little undersized. Is 17/32 inch a common seatpost bolt size for old British bikes?

[JonHouston]

it will be 1/4 BSW or 5/16 BSF hexagon. these are the same size. older spanners will say BSW (Britsh Standard Whitworth) or just Whitworth, later spanners are designated BS for British Standard, which always applied to BSF (British Standard Fine) and is one size bigger. confusing? yes. old sidchrome spanners can often be found at swap meets and junk shops. usually quite cheap because no one knows what they fit. old British cars, push bikes, aeroplanes and power stations!

[uart]

it will be 1/4 BSW or 5/16 BSF hexagon. these are the same size. older spanners will say BSW (Britsh Standard Whitworth) or just Whitworth, later spanners are designated BS for British Standard

Yeah that will be it, thanks. Both the thread size and the hex nut size measure identically to the BSF 5/16 spec.

I've got an old box of assorted spanners somewhere with a few old Whitworth in there. I'll have to take look later.

The confusing thing is that this bike doesn't look all that old. It's a made in UK Rayleigh, but it's got 5 speed shimano SIS gears. Seems weird to have a Whitworth/BSF bolt an a bike this recent - (recent being very much a relative term there. ). Maybe someone swapped out that bolt at some time.

[10speedsemiracer]

it will be 1/4 BSW or 5/16 BSF hexagon. these are the same size. older spanners will say BSW (Britsh Standard Whitworth) or just Whitworth, later spanners are designated BS for British Standard

Yeah that will be it, both the thread size and the hex nut fit BSF 5/16 exactly.

I've got an old box of assorted spanners somewhere with a few old Whitworth in there. I'll have to take look later.

The confusing thing is that this bike doesn't look all that old. It's a made in UK Rayleigh, but it's got 5 speed shimano SIS gears. Seems weird to have a Whitworth bolt an a bike this recent - (recent being very much a relative term there. ). Maybe someone swapped out that bolt at some time.

Possible retrofit of the gears, although have seen SIS on a Raleigh before, however there was more SunTour around than Shimano, on Australian Raleighs that is.

Just wait 'til you get to the BB and headset. (tip, don't start ordering cartridge BBs just yet).