Start With Identification
Ask how the supplier confirms the variant. A supplier who quotes from a partial code without asking a question is guessing. We read the code back in writing before quoting for exactly this reason.
Ask Whether Sets Are Matched
A rotary group sold as a set should be lapped and matched as one group. Parts boxed together are not the same thing as parts matched together. Ask the question directly.
Ask About Materials and Heat Treatment
Ask what steel grade is used and what the heat treatment route is, and whether a material certificate and hardness report are available. A supplier who cannot answer is not controlling it.
Ask When the Critical Faces Are Finished
Faces ground and lapped after heat treatment stay in tolerance. Faces finished before it do not. This one question separates a lot of suppliers.
Look At the Packing
Oiled and vacuum sealed parts arrive fit to fit. Parts in a plastic bag with a cable tie arrive with surface rust, and a lapped face with rust on it is scrap.
Check What Happens Afterwards
Warranty terms, and whether there is somebody to talk to about fitting and start up. Most repeat failures are fitting and contamination problems, and a supplier who helps with those saves you more than the price difference.
Compare Total Cost Not Part Price
The part price is the small number. Downtime, labour and a second repair are the large ones. A part that costs a little more and lasts twice as long is not a more expensive part.
