The 9N, 2N, and early 8N fender to axle bolts are 5/8-18 x 5-9/16" HEX HEADs with lockwasher and hex nut. Figure they've been on for up to 80 years so probably fused up solid with rust. I don't bother much with a wrench. If it won't budge after a few days of soaking in PB, I just get out my NUT SPLITTER (no, not the wife)and break the nut off then can punch the old bolt up thru the fender. FWIW and FYI: If you want to install Stabilizer Bars on your tractor, the brackets require longer bolts, at least 6-1/4". In 1949 Ford changed the fenders and axle trumpets from a round hole to a square hole so they could accept a carriage bolt with the square shoulder. Dennis Carpenter makes the OEM 5/8-18 carriage fender bolts, p/n 355310-KIT but note that you'll need to buy 5/8-11 carriage bolts if using stabilizer bars as they don' make fine thread carriage bolts anymore as Industry Standard.