Hi all,

I have a steel bike with the seatpost binder integrated into the seat-tube and seatstays (this is a Serotta C3S very similar to an Atlanta). One side of the binder bolt is of course tightened with a hex key, the other side is neither machined for a hex key nor is it hex-shaped to fit into the frame. Consequently it can spin freely within its side of the seatpost binder.

I got the frame used, and upon buildout I removed the binder bolt for cleaning and have since discovered that I can't fully tighten the bolt -- the "free" side of the bolt simply spins when I approach adequate torque; there is no way to keep it fixed.

I can kind-of cheat it to get it close to torque by applying (a lot of) force with my thumb and tightening the other side, but I would rather be able to get it to work properly. How can I get this nut to be stationary?

Options I've considered: 1. A dab of some kind of glue - downside is that I'll then have the damn thing glued into the frame, and I'll risk gluing the threads. 2. Dremel a slot for a large-ish standard screwdriver - downside: hackish, rust-o-riffic and possibly weak. 3. New binder bolt with allen keyholes on both sides (like the Campy one on my wife's Torpado) - downside: I have to search around for the right size, and then I'll have to carry 2 hex keys just to adjust my seatpost.

Any ideas? How was this system originally supposed to work?

Most of the suguino or Campy seatpost binder bolts i've seen have a tab under the head of the side without the hex (usually the right or non-drive side of the frame). The frame tab on that side has a slot the tab fits into to prevent rotation while you tighten the other end with a hex wrench.

If your binder bolt and/or frame don't have this arrangement, there are two possible fixes i can think of:

1. Place an external "star washer" or split lock washer under the side that wants to slip. The teeth of the washer should be enough to keep it steady as you tighten the opposite end.
2. Replace the binder bolt with a regular bolt and nut. That way you can put a wrench on each end. It won't be as pretty but it will work.

Usually friction alone is enough to hold one end, since the thread is of a smaller diameter than the flange nut. Just make sure the thread is greased and the static shoulder dry. If yours is spinning first check that it's short enough and the thread is smooth all the way to the shoulder. Sometimes on old bolts the screw is a bit stretched, bent or has a damaged thread so it binds before threading all the way.

Also check that the ears and seat tube are OK and not pinching closed before the post is tight.

BTW, in addition to the tabbed bolts, some have built in serrations on the non-turning end, and there are also 2 key versions which take an allen key at each end. This is my preferred design because there's less chance of breakage if you hold the screw end and turn the nut. I have a few of these and can sell you one at a low cost if you know the length you need between the shoulders.

Could be that bolt is bottoming out on the "free" end before the free end is able to tighten up onto the 'keyed' part of the frame. This happened when I replaced a similar binder bolt on my wife's old Bianchi. The new bolt was too long and was bottoming out, and I wasn't able to get it tight enough to hold the seatpost in place. I had to use some washers to solve the problem.

I'm with idoru2005, check the fully compressed width of the bolt to make sure it's not bottoming out on itself:

1. remove bolt, tighten bolt-end all the way in
2. use calipers and measure inside distance between the underside nut & bolt heads
3. measure the ouside distance between the seat-binder ears

Is #3 larger than #2?


I've had good luck with using a star lockwasher between the nut and seat-binder ears. A lot of frames have a little notch on the seat-binder where the tab on the binder-bolt nut fits.

I haven't had a chance to come back to this thread until now...I did a little research. So, it gets strange...there are no identifying marks on the binder bolt...could it be the OEM Serotta bolt? Dunno. It does have a knurled/splined shoulder, supposedly to grip onto the frame, but I don't even think the splines are engaging. There is some crustified plasicky looking stuff gunking up the splines where it looks like someone may have applied putty or glue. But get this: the bolt accepts a 5mm allen, but it also accepts a T30 torx bit. Strange.

I did check to see if it was bottoming out; negative, and I can see the bolt threads inside the clamp slot.

I looked inside the left bolt-hole and the frame/lug/ear is definitely "tabbed" for the type of bolt pictured in the post above, so now I just need to find one of those in the right length. Google searches haven't pulled up anything.

Soooo, there is a mystery bolt in there now that takes T30 torx; it could be some weird Serotta thing, but it is not tabbed and the frame is, so that seems strange. I may email them to find out more, and in the meantime I'll be hunting a tabbed bolt that is less than 15mm internal length (shoulder-to-shoulder).

Edit: forget the part about the T30 torx; that's true of all 5mm allen sockets. Bonehead move