The modern soda cans are about .004", but can be thinned some by sanding. This also removes the slippery polymer coating from both sides. I sand the piece before cutting to final size, and don't worry about pushing it quite flush with the top of the lug, so it shouldn't get pushed down too far with a little care, tho the top edges can easily be flared out (and later trimed for aesthitics) with a little pry work against the to-be-hidden lowermost portion of the post.
I've also encountered many frames with seat tube openings pinched down to an apparent smaller diameter, but rather than remove any metal, I put a post only about a half of an inch in and push back using the tremendous leverage to put the ears right back to where they were before the bolt got overtightened or clamped to a too-small post. This has worked to good effect many times now, preventing post scratching without any of the metal removal that can subsequently make post slippage hard to control and lead to bent or broken bolts.
Lastly, I have noticed that posts are typically undersized to a varying degree, and a new 26.8mm Super Record post slipped while a slightly larger 26.8mm Avocet post does not, pushed into the same Raleigh Grand Sports frame.
David Snyder in rainy, dark Auburn, CA
George Jones wrote:
>
> I have the reverse of the seat stem/cluster fitting problem being
> discussed. The ID of the cluster measures 26.8 mm, and I have two stems
> with ODs measuring 26.6 mm. that I'd like to use. I figure a 0.1 mm or
> 0.003 in. shim would take up the space. Is there a manufactured 0.003
> in. shim with a lip on the top edge to hold it in place? If so, who
> sells it? If not I'll have to improvise with some brass or SS shim
> stock. I just don't want to buy a whole sheet of the stuff for the
> little I'd need. I don't have a micrometer, but maybe someone who
> has used soda can metal can tell me its thickness. Thanks