The heavy duty bolts they used to secure the Calm drilling machine. Acually 10mm not 12. There’s one nicely positioned on the apex where climbs diverge. And another further up to the left. Very sound large bolts, probably gluein, probably worth using both of them. There are quite a few on the top as well which would be useful with hangers. Some of the shotcrete comes off if you tap it with a wooden malet or softly with a metal hammer.