Brand New
Suburban Water Heater
Heating Element part #520789
1440W 120v Newer Style Screw-In  (comes with rubber o-ring/gasket)
(note: older style is bolt-on)
Please note: SAFETY NOTICE (sticker part #191800) applicable only to Suburban Water Heaters with a serial number range from: 953401118 to 974400950.
This note is included in the packaged 520789 heating element as a reminder to people that have a water heater built in 1995-1997 to be sure that they put the orifice back in the burner tube once they have taken the burner apart to get to the element.  If yours is a newer unit & has the orifice pressed into the burner than it will not be an issue and it won't fall out and this safety note is not needed in your case. If it is though, please attach the sticker to the water heater compartment housing to where it will be visible when door is open, for future safety precautions. Thank you!
Q&A
what is the thread size?
According to Suburban the thread size is 11.5 NPSA.  I tried looking up what NPSA meant and am finding nothing giving me a measurement chart/breakdown.  Suburban has 3 styles of elements they use.  The older ones are bolt on and the newer ones are screw in.  The 6 and 10 gallon SW series use the  520789 where as the 12 and 16 use the 520790 (a bit longer). 

6 1/2" in length.  The screw in portion is 1 1/2" diameter.  It is intended to be submerged in the water or it will burn out withing a few seconds.