The British gaskets I have are some sort of fibre rather than cork, probably as an economy measure. The mounting plate appears to be the same fitting though: 9-in square with 8 holes to fix it to the vehicle. (Mine is ZA.21282 Panels, Mounting, No.8 and 9-in square x 3/8-in thick with a 3/4-in central hole for the feeder cable (or extension bar) and six countersunk holes to match Insulator W/T 'H' - the bottom part of a complicated arrangement using an Aerial Base No.3 for flexibility and Aerial Rods 'D' for the actual antenna[1].)
Chris.
[1] the 34-ft "Steel Vertical Aerial". This required extra support to prevent collapse of the rubber 'dome' of Base No.3, and I finally got one of those brackets from Geoff Truscott after searching for one in the UK for a couple of decades!
