A brass round lug is screwed up and screwed down from separate brass fittings top and bottom on the door. They remind me of a brass ballcock in a cold water storage tank. You need large spanners 1 1/4 if I remember, to tighten them up in the correct position to get the door closing correctly, but once the fittings top and bottom are set in the right places, the door can be removed very easily by a square 1/2" top and bottom which screws in and out and it is locked in place by a large lock nut.
To put the door back, just screw them back in top and bottom, and if you have left the large nuts in their places, the door will not need any adjustment.
When taking the door off, I lay underneath, and put 4 cushions on the concrete to lay the door down when it was released.
You can do up the two square 1/2" lugs top and bottom by hand until they locate in the holes in the door surround, and then the door will self support. Then lie underneath and do up the square 1/2" lugs but you have to reverse the spanner every turn, as with 4 sides, there is not enough room for the spanner (wrench) unless you cut it down. I used WD40 on the lugs to make them easier to initially locate them in the holes by hand tightening.
