The nos clubman door cards I have bought. I'm sure I remember atleast one having a hole there for a screw (think it may have been a late model card) but most did not.

So thinking most holes have been put there by the owners to help hold the door card in position.

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Round nose minis with wind up windows have 2 small countersunk type screws with cup washers. Not sure about Clubmans? I think they had none or maybe one?

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

My '73 Leyland Mini S had them from new. I remember them (complete with their washer) from when I removed and refitted the cards and I know I certainly never retrofitted them. Not so sure about the '71 MIni K, but since it had the same doors I wouldn't be surprised if it also had them. But I am pretty sure there was only one on each side.

If you're talking about doors for round-nosed minis with external lever type door handles (not the clubman recessed handles) - there are "clip things" at the front edge and there are 2 screws that fix the trailing edge (nearest to striker plate) of the doorcards to the frame. They are about 4 (or 6) gauge countersunk headed screws fitted with cup washers that screw into small holes in the door frame.
I will check on exact screw size later if you need it.
Bill.

The screw method looks pretty dodgy, but is factory original. Just had a look at my most convenient car - screws are 4 gauge (about 1/8 inch (3.5mm) diameter) x 3/8 inch long with countersunk head (tapered sides, flat surface - not domed surface) with posidrive pattern head. Phillips head will work ok as posidrive is hard to find. I think these screws are the same as the screws used on the hinges for the rear quarter light windows. The cup washers are available from hardware stores - their sizes are the same as the screws they fit - i.e. No 4 washers for 4gg screws.
Interesting little question.
Bill