They are 38mm .... the company that sells them are useless ... dresser bars is just another name for crash bars ..... luckily I only bought these to use to make jigs using the mounting points .... they sent them in a box with no packaging from Germany to England so you can imagine what they looked like when they turned up ....the mounting brackets are so thick that they supply a piece of threaded studding to use as a replacement engine spindle .... lots of nuts and bolts (some which were missing as they just chucked them in a plastic bag in the box which was split ) .... no instructions to show where the bolts / spacers go ..... they are **** really ... they don’t even line up in the same position when they are on the bike