Could be a 5mm one that's worn, could be 7/32". Try to get hold of a 7/32" imperial allen key or a 5.5mm metric one (they do exist).
@Bearlegged started
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Could be a 5mm one that's worn, could be 7/32".
Try to get hold of a 7/32" imperial allen key or a 5.5mm metric one (they do exist).