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I noticed there are two very small holes on both blades on my new fork. They are on the inner side of the blades at the end of the fork blade just above wheel axis mounting point. They are apparently designed to put there because they are at the same position and holes are smooth and no damage. So what the purpose of these holes? I noticed that my old fork also got similar holes, which I never noticed before.

  • If your fork is metal, which you don't mention, the holes are vent holes for the brazing process. They evacuate the fumes and prevent pressure build-up during brazing. – Carel Mar 4 '16 at 11:23
  • Yes it's steel. That's interesting, can you explain more and put it in the answers? Do I need to cover the holes using duct tape to prevent rain from getting in? – thotwielder Mar 4 '16 at 12:25
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    The holes are either vent/drain holes or holes for "lawyer lip" washers to retain the wheel if the skewer comes loose. (If they're vent/drain holes and you cover them you will prevent rain from getting OUT.) – Daniel R Hicks Mar 4 '16 at 12:51
  • Clarification request - can you see through these holes or are they into the closed space of the front fork? Trying to understand if they're axle-retaining washer hook holes through the lugs where the wheel mounts, or if they're above that and into the hollow of the fork itself. – Criggie Mar 5 '16 at 2:56
  • @Criggie it's into the 'hollow'. Can't see through. It's above the wheel axis mounting point. Very tiny hole, about 1 - 2 mm in diameter. – thotwielder Mar 7 '16 at 9:40
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On steel forks the tiny holes at the bottom end of the fork-blade are vent holes for the brazing process. The brazing produces fumes the fumes and the heat expands the air in the blade which makes that these holes are needed to evacuate both. On steel frames you may find similar holes in the seat-stays and in the chain-stays where they are usually close to rear drop-outs. If you're worried about rusting because of moisture that could go inside spray some wax-coating or tar-based antirust inside, or a periodic jet of penetrating oil as I do.

  • I have them in my carbon fork too. I'm pretty sure they didn't braze anything onto it. What are the holes for in a Carbon fibre fork? – ShemSeger Mar 4 '16 at 14:12
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    Same reason @ShemSeger, carbon forks and frames are bonded by baking in an oven. The air trapped inside tubes expands from the heat and would blow the tubes up. The holes are there to let it escape. – Carel Mar 4 '16 at 16:43
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These are moisture drain holes. Moisture can condense and build up inside frames and cause rusting (in steel frames) or delamination (in carbon fiber).

The drain holes allow for the built up moisture to drip off.

  • For drain holes to work 100% they should be at the very lowest point, which is usually not (or just never?) the case for the holes the OP is talking about. So which answer is correct, this one or the one by Carel? Or both (i.e. it really is about venting fumes, but also manages to drain). – stijn Mar 6 '16 at 9:47
  • I think they may also be used to drain, they are almost at the lowest part of the hollow part of the fork blades. – thotwielder Mar 7 '16 at 9:42
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Some bikes have that kind of thing to use a, kind of, washer with two tabs that locate the fork better. Not seen it on many recent bikes though. I think it's only on Non quick release type axles too.

  • Those would be axle-retaining washers which go on the axle and hook into holes in the flat part of the fork. I read the original question to mean holes in the fork part, but on re-reading your answer makes sense too. +1 – Criggie Mar 5 '16 at 2:54
  • OP's comment shows that they meant a hole into the hollow of the fork, so this is not the answer to OP's question. Still a good thought. – Criggie Mar 7 '16 at 23:00

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