Seatpost binder bolt with threads in the frame

[torqueless]

Re:

5.5mm is I think within 3 thou of 7/32"- and in this case the metric size is the smaller. In other words, a 5.5mm key would probably be functional in a 7/32" socket.


Back to the thread in the OP's frame-
the dimension charts for thread standards usually include a 'tap drill' size.

The OP could try the shank of a drill bit in the hole:

A 5.5mm or 7/32" drill bit will not pass through a 1/4" BSF nut, and it will also not pass through the thread in my binder bolt housing.
A 5mm drill bit will pass through.
I know that empirically 'cause I just tried it..

Incidentally the same is true for an M6 nut.
I know that empirically 'cause I just tried it..

I don't have an M7 or 5/16" nut to hand. Perhaps someone could try the same drill bit shank experiment on their 5/16" threaded hole, and report back with 'go' and 'no go' diameters?

Edit: I just dug out a 5/16" BSF nut and bolt. Afaict, these diameters will pass freely through the nut: 1/4", 6.5mm
These will not: 17/64", 7mm

Incidentally 6.5mm will not pass freely through a 5/16" BSW nut.

 

[CBguy]

I have cable tied the Allen key for the seat bolt to the frame, it's an odd non-metric size and don't want to lose it...... Perhaps it's a 3/16 th

Shaun,

The integral seat bolt arrangement on your Thame Cronometro looks, to these old eyes, very much like my Claud Butler (other than shot in stays). Interesting to know if that zip tied Allen key is actually 7/32 and bolt a 5/16"/22tpi BSF as mine? Perhaps your Woodrup is similar? If so that would go a long way to saying, although unusual in today's world, this seat bolt would have been common back in the day.

Doug

 

[CBguy]

Re: Re:

That style seat clamp is used on my Clive Stuart frame. Ken Bird and Bill Gray were part of that group.
I believe a 5.5 mm hex wrench is the head size, Don't know the thread pitch.

Hi Curyam,

Interesting, if able I wonder likewise with my last post re Midlife's frame, if bolt size might be same as with your Clive Stuart?

Doug

 

[Midlife]

Hi Doug

I'll have a look at the Holdsworth Chronometro seat bolt tonight when I feed the guinea pig LOL

Shaun

 

[Midlife]

Fleeting garage visit to feed "Fluffy", pulled the seat bolts from the Chronometro and the Woodrup (aka Kevin Sayles Jackson) and they have bolts the same as Doug's. Knurled recessed land, identical small chamfer etc. Both late 60's to early 70's.

I've got a few more later frames that l'll check ...3 x Aende, Holdsworth Classic, Rourke, Andy Thompson, Raleigh... however I think the bolts are smaller in diameter and take a smaller Allen key?

Interesting lol

 

[CBguy]

Shaun,

Wow, I wasn't quite sure what "feed the guinea pig" meant. Thought might have been some sort of idiom as "raining cats and dogs" that I wasn't up to date on and was afraid to ask. Didn't guess literally "feeding...

Did you try a 7/32 Allen key, measurements or do you just know?

Thanks for the effort and info!

Doug

 

[torqueless]

Re:

I hope, for Fluffy's sake, that you use a larger spoon to measure his dinner than the one you use to feed us seat bolt dimensions..

 

[torqueless]

Re:

BSF-centric info- I have no idea whether it applies to other 'imperial' hex-socket bolts:

The binder bolt on my '75 frame is:

1/4" x 26tpi BSF.
The threaded part of the bolt is 5/8" long.
The hex-socket is 3/16" across flats.
The outer diameter of the head is 23/64" (ie it fits snugly in the socket marked 23/64" of an old 'imperial' drill bit stand)

The equivalent 5/16" bolt is:

5/16" x 22tpi BSF.
The threaded part of the bolt is 3/4" long.
The hex-socket is 7/32" across flats.
The outer diameter of the head is 27/64" (ie it fits snugly in the socket marked 27/64" of an old 'imperial' drill bit stand)

The shank of a 23/64" (or metric equivalent) drill bit will fit (with some clearance) the socket of a binder bolt housing designed to take a 1/4" BSF hex-socket bolt.

The shank of a 27/64" (or metric equivalent) drill bit will fit (with some clearance) the socket of a binder bolt housing designed to take a 5/16" BSF hex-socket bolt

The head of a 5/16" BSF hex-socket bolt will not fit in the socket of a binder bolt housing designed to take a 1/4" BSF hex-socket bolt.