Is this 15mm as stated or 15.8mm? I need it for belle mixer. You have 2 GXH50 engines on site, what is the difference?

Thank you for your email, the GXH50 for the mixer is GXH50 QXB4, I have included the link below; https://www.lsengineers.co.uk/honda-gxh50u-qxb4-engine-suitable-for-belle-minimix-150.html