<VV> Aftermarket parts (little or no Corvair)

[NicolCS@aol.com]

One of my clients (I do technical editing for auto companies) posed an 
interesting question to me;  I'm sure there are some on the list that have the 
answer and I think the topic will be an interesting thread.  Here's the question: 
Where to makers of aftermarket parts (for example; fuel pumps, sensors, wheel 
cylinders) get their specifications?  Do they reverse engineer OE parts? Do 
they obtain specifications from the OEM?  Do they merely re-label parts from 
other makers?  Also, I kinda remember something about the OEMs being legally 
required to provide specifications to aftermarket makers?  Anyone know about how 
this works?
TIA
Craig Nicol