decoding a 59 rim

[Tod59]

Hey guys, I took the tire off the rim on my 59 short fleetside and found the stamping inside the wheel. The stamping looks like:
Made in USA 15x55k NT D9

Can anyone help me decode this? I believe the 15x55 relates to the rim size for sure, I think it's supposed to be 15x5.5 and im not sure what the K refers to. I believe the last number D9, may relate to the month and year???? April, 1959? I think NT may relate to the light duty 1/2 ton truck?
Any ideas or opinions very helpful.
Thanks,
Tod

[chopit]

http://www.348-409.com/wheelchart.htm

I found link searching 15x5.5k NT D9

its for cars not trucks but shows NT to be the manufacturer (Norris Technologies)