Wanted: (Campag) seatpost bolt, 21mm-ish and some advice

Over-torqued my seatpost bolt when adjusting my saddle height mid-ride after swapping out cranks, and had to ride 10 miles back with the seatpost all the way down. A few questions:

1. I’m hoping I wouldn’t have damaged the frame by riding a saddle without a seatpost bolt? It’s 753 tubing with an alu seatpost if that helps.
   
2. Is there any reason why I need to replace this with a campag bolt? They are frightfully expensive (£30 for a bolt on eBay seems like daylight robbery) so I’m wondering if there are cheaper alternatives for steel frames which might work in its place (I see unbranded ones on eBay for a fiver)? Would be fairly keen on a non-QR one to deter opportunistic theft; I liked the fact that the Campag bolt needed two Allen keys.
   
3. Anyone got one for sale? Think my seatpost spacing was about 21mm long based on the snapped pieces, and think the inner diameter of the seatpost hole is just under 8mm (my 8mm Allen key does not fit in the space, but just about).
   
   

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I might be wrong but I think are designed to snap if you tighten them too hard , or at least the Campag ones are easily broken . I just measured and bought the best looking bolt in correct size on eBay, so not a campy one as agree they seem pricey.

Have discovered to my chagrin. Condor seems very reasonably priced so may swing by their store to try to buy one!

https://www.condorcycles.com/collections/seat-clamps-spares/products/condor-seat-clamp-bolt-binder-bolt?variant=44762146898241

Have you any idea if I should be getting the 19mm instead of the 22mm, given that my seatpost internal diameter seems to be just over 21 but not 22?

Yep that will do it . Have you got the old one to take in? Going to be frame specific - based on the size of the seat cluster .

Is that condor one alloy? Sugino are chrome steel and have nice deep Allen key slots. Unusual for an expensive 753 frame not to have a threaded seat lug.

Yeah it's alloy - does that make very much of a difference? The Campag steel one snapped on me regardless - and the eBay one is CrMo! Also inclined towards the Condor one simply because I can swing by their shop tomorrow to pick one up rather than having to pay twice over for shipping (then waiting a few days to get back on the bike).

Frame is a Bob Jackson of 1990s vintage (guessing from the DT shifter bosses and tubeset, but don't actually know provenance as bought as a frame off someone here) - no idea why the seat lug is not threaded.

Get a steel one. There is no point in an alloy one, too fragile and the weight saving is marginal to the nth! There was a batch of Campag ones that were made out of cheese, I had one fly off mid ride a few years back, didn't event touch it. A close look at a selection revealed some weren't properly radiused where the thread ends, which creates a weak stress point. Sugino or generic CroMo ftw. The length you need is nothing to do with seatpost diameter inside or out. You want about 3-4mm less than the overall width of the frame lug where it will be inserted - measuring with a tape/ruler is accurate enough. If the seatbolt is too long it will bottom out on itself before the seatpost is clamped tight enough (or at all). If it's too short you risk stripping the threads when you tighten it.

Thanks all - will go find a generic CroMo in that case!