The length depends on where the retaining nut is in the stock. With the action out of the stock look on the bottom where the front band would be and if you see a brass nut sunk into the wood it is a 10" rod. If not, then turn the stock over and look in the barrel channel about 2.5" back from the front band and the brass nut should be there and you need a 12.5" rod. Original rods the threaded part has a slight point, and the loop area where the patch goes is more rounded. Reproductions are usually flat on the end of the threads and the patch area is more square and may look like new metal.
Wineman