Stem bolt important?

I've got a cinelli quill stem, 26mm (maybe 26.4mm) and nitto br-021s, 26mm.

The bolt on the stem is missing, so I got a nut and bolt from work and fitted the bars. Now however tight I go, and even with a coke can(s) for a shim, I can still cause the bars to slip with a reasonable force, i.e. just leaning on them heavily.

Does it matter that I'm using an ad-hoc bolt/nut?

Ffs...

I'm no expert but I think the answer is in your question.

Thank you for the prompt replies.

I'm no expert but I think the answer is in your question.

What? the stem size, or the bolt, or the force?

-I thought 0.4 mm wouldn't be a problem with the use of a shim
-I tried both my LBS if they had a replacement bolt to no avail. Clearly I will get a correct bolt, but why shouldn't a generic bolt work for now?
-When I say a heavy lean, I'm overstating it, it's easily enough that I wouldn't feel comfortable riding.

apologies for tardyness

a generic bolt shouldn't matter, sounds like you are not shimmying enough

try dr. pepper

I managed to get a replacement stem bolt for a Cinelli stem from Finsbury Cycles on Seven Sisters Rd

Been recommended Clerkenwell Screws as the place to get unusual or hard to get screws, bolts, etc.

The bolt is not the problem, as mentioned, your shim is probably inadequate.

Buy a shim or use more tin can.

Wait... You're using a NUT and a BOLT in a stem, where, presumably, just a hex headed bolt existed previously, PLUS bars that are under sized?

I dare say the combination of these factors is leading to a terrible interface between the stem and the bars, plus a lack of adequate clamping force.

i'm not even going to honor this thread with a post.

try dr. pepper

how good is dr.pepper

beercans!

Weight weenies will be using Diet Coke cans, obviously.....
S.