I always seem to need short or shims so got some cut.....1mm or 1.5mm 316 grade stainless steel. The holes in engine mounts are about 10mm and bolts only 8mm so a bit of slop there...if you push your mounts hard out towards the sides of the hull when you install (so they cant shift during use) you may find you need extra shims... 0.5mm = $2ea 1mm = $2.50ea 1.5mm = $3ea