Lost my arbor nut........ (Don't even ask) as near I can figure it's a left hand 1/ 2-21 thread per inch. McMaster Carr has them 5-6 per bag for approx $6 per bag + shipping. Am I right? Good tip....... if you do a minimum amount of grinding down below you can fit harbor freight carbide tipped 8-5/8 diameter blades that were $5.00 + each 5 years ago. Only problem is that the blade won't fully retract to be flush with the table top. Build yourself a small sled and you will be in heaven...... how about what thread count on the arbor, guy's. My 103's doa until I get my nut' s. Pardon the expression..........