The grub screw is M5 use a good quality or new allen/hex key or you will risk rounding over the edges of the grub screw and then will have to drill them out I replaced mine with stainless steel.

I think these are the head light units price per pair
https://www.s-v-c.co.uk/product/7--free-standing-black/


2021 M3W
2013 M3W - Sold
1971 4/4 2 Seater
1934 Sports