FL1 TD4 Injector Cap Size

Hi folks.
One glow plug has refused to come out, or drill nicely, so decided to remove the head and safely knock it out from the inside. Unfortunately that means getting the injectors out, which are refusing the well documented prise or wiggle methods. I've bought a slotted window socket set to remove the caps and attach a slide hammer, but the 29mm just clears the plastic cap - then spins on the nut. 27mm won't clear the plastic.

BMW M47 posts seem to state 27mm cap.............. I'm confused ! Any thoughts ?

Many thanks,
Tommy

Depending on your reason to remove glow plugs, the M47 engine will start with just 3 glow plugs. May get a bit f white smoke until fully firing.