Hello Dave.
As Brian says the gears are 16 DP, the set of ten also listed by Brian were available when the lathes were made. The list is on lathes.co.uk, but under the name EW. It is worth reading. I assume that your lathe is fitted with back gear as it is the model D. For gears you either use 16 DP gears available from HPC Gears. They are expensive to put it mildly. Or you can use 20 DP Myford gears, much cheaper and available on ebay. A design was put online to use them for fine feed by a contributor also describing updating the lathe. Put 'STRINGER EW LATHE' into Google, look and read.
The leadscrew is 8 TPI, unfortunately it is right handed which makes fine feed impossible using the 16 DP gears. Again a modification was published in ME by J W Constable many years ago using two extra gears.
I am in the process of getting one of my EW lathes running. I found it beyond belief that a lathe designed and built post WW 2 used Whitworth threads throughout. It is a substantial machine, but some design features make you tear your hair out.
I wish you success with your lathe.
Mike Potts.