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If there's a better forum for this please let me know. I have a steel frame hardtail mtb that tipped over and has a minor dent in the top tube. I've been reading about using tube/frame blocks to partially work the dent out and was looking for advice. I measure the top tub diameter as 35.1-35.4 mm (depending on location of calipers there is slight variation), and this is measuring over a coat of paint. Available frame blocks from a website called paragon measure either 34.93 mm or 36 mm. Which would be best? I'm torn because 34.93 is very close, but smaller, and 36 is bigger, but we're talking less than a mm in diameter difference.
 

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34.93 mm = 1-3/8" (1.375") which is mosty likely what your unpainted tube diameter nominally measures. The dent is unlikely to roll/pop out if the tube blocks are not a very tight fit to the tube, I dont think that the larger 36mm size would do anything. You might loose some paint with tight metal blocks but it is more likely to help with popping the dent. Note that you can also make your own tube blocks from a 4" block of hard wood such as oak using a forstner drill bit and drill press. Actually works better/stronger if you laminate together several 1" boards glued and clamped together with grain oriented at 90° so it is less likely to split that a block from a solid piece of wood. Once you bore through with the forstner bit, use a saw to split the block into 2 pieces. Wood blocks are nice because they are less likely to scratch the paint than metal blocks.
Minor dent in TT is not really structural, you can also fill it with J-B weld epoxy then smooth and paint (or cover with a sticker) to restore cosmetically.
 

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furker
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Are you planning on using the rolling method and then repainting? If so, strip the paint first and remeasure. The rolling method will damage the paint anyways. The 34.93 is probably the winner. The 36mm will bottom out in the vice too soon before it can do it's job.
 

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furker
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Paul B. could have used some wax or other lube with those brand new blocks, until they were nicely worn in like his others... He was making his job harder than it needed to be, so that he didn't need to use that much force to roll it. But he has far far more experience than me.
 
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