What spec do you want to know? typically the we are interested in whether or not it is heavy duty or standard. Standard is roughly 4-10#s and hd 12-18 or there-abouts. The concern would be whether or not it's for a t/a style or t/e style, etc turbo and would need a special bracket welded to fit properly.
This is an attempt to get this thread to become a "sticky"
Title: How to Test WG Actuators
Tools and supplies needed : air compressor with air flow control and hoses.
Test 1. Wastegate removed
a. Apply compressed air to actuator port slowly increasing it.
b. Note psi setting when diaphragm movement is detected.
This test will give you an approximation of the spring pressure inside your mystery actuator.
Test 2. Wastegate installed
a. Remove hose from port
b. Disconnect actuator rod from wastegate
c. perform a and b from Test 1
There are too many actuators out there to accurately identify. Using air pressure with a gauge would give some info about what it is. A scale could also be used to measure the spring tension but then it would have to be compared to the size of the diaphragm. For it to be a sticky the actuators would have to be identifiable and tested so that others could use
the info in the thread to identify what they have.