My scooter calls for "#6 and #5 Allen key", I can't figure out what sizes (in inches or mm) these translate into. I know I need to buy an allen set, but wanted to make sure it has the two sizes I need before purchase. I think this may be 5mm and 6mm, but thought it was a really funny way to phrase that, so I was hoping for confirmation.


The #5 Allen key is for the brakes and #6 is for the handlebar.

  • I would guess they are 5mm and 6mm, though those seem pretty large for the application. Can you take the pieces down to the hardware store and try them? The sets with the allen keys hinged into a handle like thisare usually accessible on the shelf. – Ross Millikan Mar 18 '17 at 16:46
  • @Ross my brakes all need a 5mm even if they need something else as well. 6mm is large for modern headsets but with a quill stem it's normal – Chris H Mar 18 '17 at 17:17
  • @ChrisH: good point. I find I use 3mm most often and smaller more than larger, but my metric sets have them all with no problem. – Ross Millikan Mar 18 '17 at 17:19
  • Every bike owner that does any of his own maintenance should have a set of allen wrenches. Most bike shops will sell a set that is built into a handle like a Swiss Army Knife, and this is a very convenient form, and not terribly expensive. – Daniel R Hicks Mar 19 '17 at 12:42

'#5 would be 5 mm
10 mm = 1 cm

Most bike shops will have kits / tools with those sizes
Those are very common bicycle sizes

This tool has 4, 5, and 6

  • 1
    You mean the #5 would be a 5mm key? Is the #6 a 6 mm key then? – gschenk Mar 18 '17 at 18:19
  • @gschenk Yes that would be correct – paparazzo Mar 18 '17 at 18:20

See norm DIN 912 / ISO 4762 - the relevant number for the tool head is s given in millimetre: s=5mm (M6) and s=6mm (M8). The '#6' Allen key has a 6mm wide head and fits M8 screws and likewise the '#5' Allen key has a 5mm wide head and fits M6 screws - so there is room for some confusion here.

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  • 1
    Could you elaborate what this means in terms of the original question? As is, this answer could be interpreted to mean that a "#5" hex key would be for M5 screws (so 4mm tool size). This seems unlikely to be the correct interpretation. – Emil Mar 22 '17 at 11:36
  • 1
    I updated my answer. – Christian Lindig Mar 25 '17 at 19:04

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