There isn't one. There's tons of different numbers on the part, Seimens made it. Everyone I speak to knows exactly what it is and yards have told me that it is a Merc Scam to force you to buy a complete unit just to get a heat switch.
Some of the numbers...
5
5/2
9 140 010 281
539 9879 770
then theres 944 in a box
LOL! all these on the top of a box measuring about 2" long by 1" wide