AC has a code system for their spark plugs. The difference between the two plugs is that one has an extended tip and the other does not.
R44TS
R= Resistor
4= 14 MM
4= Heat range
T= Tapered seat
S= Extended tip
The R44T is the same plug except it does not have the extended tip.
For further information, check this site out.
Jim
http://www.acdelco.com/html/pi_plugs_ident.htm