Custom engine ring mount shims - note not used

Source of stainless steel tube:

11mm x 0.5mm x 400mm 304 Stainless Steel Tube for Industry Machinery | eBay Australia

I made sure the tube was seamless in construction. Some thin-walled tubing that is available has a welded seam.

When I finally mount the engine I will smear this tubing lightly with Duralac yellow to remove any issues with stainless steel/mild steel contact

EDIT: 250728

I have had a discussion with a Rotax dealer technician who has advised the 0.5mm gap between the M10 bolt shoulder and the ring mount diameter serves two roles: extra protection of the bolt against impulsive shear loading in the event of a rubber hard-stop, by allowing movement; allowance for tolerance in the engine mounting frame. The most common mode of bolt failure under impulsive shear loads is fracture.

For the above two reasons I have decided to OMIT these stainless steel tubes