Both what I had in mind too, but I'll add that if (owain) you're not aware the 'bolt' which is also a 'nut', also has a left hand thread, which does the extracting, so you need to turn the 'nut' until it disengages and spins free- then push it to engage the armature and it'll screw on (that's GB's 'BSA Magic' )..something along those lines
If I'm describing how to suck eggs let me know, I haven't had brekky yet