In the early years Douglas invariably used odd gauge spokes i.e.13 , 11, 9. However,11 gauge has not been available for some years. Spoke dies are easily and cheaply available for cutting threads but you may have difficulty finding nipples to fit properly as spoke dies cut the thread to the same diameter as the spoke while the correct means of threading spokes is by rolling the thread. This throws up the metal to a larger diameter than the gauge. It also has superior strength as a cut thread acts as a stress raiser while the rolled thread allows the grain of the metal to follow the contour of the thread. Nipples as supplied are made to fit rolled thread spokes as far as the internal thread is concerned. As for the nipple not fitting the hole in the rim, this should not be a problem as nipples are available in a range of diameters externally to suit the holes in the rim.
A few years ago thread rolling equipment while not exactly easy to procure, as it tends to be "trade" equipment, was actually available. In the meantime the market has been flooded with far eastern imports and spoke threads have become metricated. (They are even calling 3mm, 12gauge but although almost identical in diameter has a different number of threads to the inch). It is now extremely difficult to find imperial wire gauge thread rolling equipment and when it can be found the prices have rocketed making it uneconomic to consider unless you are going to cut a very large number of spokes. I buy my spokes in bulk (250 at a time) cut to length and thread to suit the rims and belt rims. There have been large cost benefits compared to ordering threaded spoke sets but you would not break even now if you are only going to do say four wheels with the current prices of the equipment.
I am not 100% certain what gauge was originally fitted to the TS model, probably 11 gauge in which case 10 gauge is too large and as you have found, to use this gauge will necessitate drilling out the holes on the hub and enlarging the countersinks to receive the head of the spoke. Some restorers have gone down this route.
I have opted for 12 gauge on all my 2.3/4hp restorations and believe this to be adequate for machines of this era with the power available and limited speeds to be used. My veteran only uses 13 gauge.
Whatever you decide you should replace the whole wheel set of spokes.
