Where do I find the model number??

And more here with a link to the User Manual (70 pages pdf)

http://forum.kitchenaid.com/forums/topic.asp?TOPIC_ID=21293

K4 models seem to mean 4 1/2 quarts bowl capacity and
K5 seems to be 5 quarts

Peccavi
February 2009

This text...

"I have an older-looking K45, but I can't find a serial number. Mine has the model number and volts, etc. stamped into the metal base plate that the bowl locks into. It says it was manufactured by Hobart in Troy, Ohio. It also says DC to 60 cycles AC on it. 115 volts, 250 watts. It's got the stainless steel bowl and the burnished beater. Any idea how old it is? Oh, if you turn it over, underneath it has the number T-77720 stamped into the metal."

Came from this site...

http://forum.kitchenaid.com/forums/topic.asp?TOPIC_ID=8049

Second post from the bottom

Peccavi
February 2009