I concur with everything fryboy says...and I will add I have two #1 units with the Square drive pressure screw, threads on those are alike...BUT different than the many 45's I have. The brass sleeve on the pressure nut isn't notched like the brass sleeve on the 45's...the #1 brass sleeve end's are butted together...and tend to leak easier.
I'll add even more, if you are ordering a pressure nut, I'd order a pressure screw as well, it's so cheap compared to the postage and it's good to have a spare laying around.
Now, I always use a heater...even on the warmest days, I use a 200Watt megnetic auto engine heater. It will run constantly, so "I" am the thermostat. I find that once the sizer is at the correct temp, I can shut the heater off and usually stays warm enough til I'm done sizing...unless it's a cold day or I get distracted with another task.
I use to use a thrift store clothes iron with a thermostat, but it's so much larger than this mag engine heater, and gets in the way.