Yes , Stainless hollow bolts , well spotted Neil
There was a little bit of chat on here a short time back about the two hollow bolts that go either side of the cylinder head. They hold the tinware in place and have the hole through them to allow exhaust gasses to escape if your head gasket blows rather than the gasses going into the car heating system. I have had a few problems with these bolts partly because they have a habit of seizing in the head and I am not sure if they are cast steel as the hex head is not too accurate and a spanner will slip quite easily. They are odd little bolts as the thead is M10 but they have an M8 size hex head. I did think about drilling some M10 bolts but the head with a washer would have been a bit big so just hit on the idea of using a suitable stainless socket . Seems to work quite well
