What size of wrench do I need to adjust the trigger on a pre-64 winchester? Thanks Ron

Actually you need two and a very fine screw driver. I use my Starrett scale as the screw driver and the wrench size that I use is an 8mm

A pair of quarter inch wrenches should do it, and as Vapodog mentioned, a very thin screw driver for the end of the threaded rod. The wrenches from Brownells are really thin, but I wouldn't buy them again, as one of them broke with only slight pressure.....too brittle, I guess. I would look for some ignition wrenches at a tool store and grind to a thinner profile if needed.