Mafrac calipers I've used stop as well as Weinmanns, but are a bit harder to set up.
I don't like the levers though, as the reach is too long for my stubby fingers.
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(who has trouble with N-frame S&Ws as well).
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You know it's going to be a good day when the stem and seatpost come right out.
(looking for a picture and not seeing it? Thank the Photobucket fiasco.PM me and I'll link it up.)