Nick, rather than email you directly I’ll try and go through this on the forum in case others have the same problem in the future. My camera has issues so all photos are taken on my mobile telephone hence there may be quality issues or pictures upside down. The yoke cap is fixed on with a clip, after removing the cap you are presented with an outer retainer on the hub. Beyond this at the other end is the bottom of the hub which is affixed to the column by 4 bolts. This end where the bolt holes are located is 11mm thick, so logic says that this is also the depth of your bolt holes. Pictures attached hope it helps. The last two photos are taken from the rear of the yoke.

Nimrod yokes

Also while I am at it,
ex-mod-aircraftspares.com are selling the new type co pilots RAF Nimrod control yokes.

Its post war 50’s to 60’s, very difficult to pin it to a particular aircraft as it would be a standard fit. I’ve seen very similar on Percival Pembroke and Percival
prince cockpits but no doubt fitted to many more types of aircraft.

Ian, No unfortunately I did not win the picture but its the only full one I’ve ever seen of the Tudor. I too like the large Avro yokes and especially would like to get hold of a Tudor and Hermes I except the latter is not from the same stables but still the same ilk of early British passenger aircraft. The HP42 would be the absolute holy grail for me though!
I hasten to add that I am always on the look out for early civilian airliner yokes and would happily swap some of my WWII yokes against them if anyone out there has any?

Not York but good guess, here is a more complete picture.

Graham has just listed a nice Halifax yoke.

Have you tried http://www.airliners.net ?