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I have lost the fixtures required to attach a bike rack.

The hole at the bottom of the rack has a diameter of 6 mm. It requires an adapter which sits in that 6 mm hole so that a M5 bolt fits snugly.

I have been trying to search for a replacement adapter, but do not know a good term to search for. Does anyone know the name of this particular kind of adapter?

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    "collar" would be one word to describe it. I've seen the same used to mount a presta valve in a schrader rim hole, albeit with different dimensions. Any machinist should be able lto ship this up from a suitable sized bolt, using a drill press. Once its made, do use something to hold it on the rack - some 2 part epoxy between the collar and the rack would be ideal to stop it getting lost. – Criggie Jul 24 '18 at 0:23
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One of my racks has similar oversize holes and just doing the bolt up tight is fine, with a washer under the head. Some clearance in fact is necessary (the typical clearance hole for M5 is 5.5 mm). I've also seen plastic spacers in this role. If you find it needs just a little something to fill most of the gap, heatshrink sleeving might do the trick, again with a washer under the screw head, as the spacer is centring rather than bearing a load. It is possible to find aluminium tube of just the right size whic could easily be cut with an adjustable pipe cutter used gently, or a hacksaw (I assume you don't have access to a lathe or this would be trivial).

  • Some 6mm outer/5mm inner plastic or metal tube cut to size? With a washer under the bolthead. – Carel Jul 24 '18 at 9:06
  • @Carel just, but you probably need at least 5.1 ID which is only a 0.5mm wall. The stockholder we use here doesn't have it, and nor do my regular eBay suppliers, but I have found a source – Chris H Jul 24 '18 at 9:23
  • Great thinking. Some layers of nylon/hemp plumbers tape would fill the gap nicely too. – Criggie Jul 24 '18 at 9:40
  • In the case of a metal tube, a thin round file might remove enough material to make the bolts fit. Same with hard plastic tubing. With a soft tube I'd cut it longitudinally and remove a sliver from the wall. The idea is to fill the gap between 5mm bolt and 6mm hole, there's no need for precision work. – Carel Jul 24 '18 at 14:50
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    @Carel with aluminium you might get away with filing half a mm off the inside of typical tube using a needle file, or drilling first then filing if you've got a suitable vice. I've had less success with many plastics, and can't really recommend trying. – Chris H Jul 24 '18 at 16:23
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What you are looking for is a bolt spacer. If you google "M5 bolt spacer" you should see a few options.

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    Options I see on google don’t seem to have the lip illustrated in the question. So washer under the bolt head as well? – Swifty Jul 24 '18 at 8:24

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