Here’s a quick overview of average males, so maybe call that STR 7-8 depending whether you factor in dimorphism.
Learn how much the average man can squat, bench press, deadlift, overhead press, and barbell curl. The numbers may surprise you.
outlift.com
Doing a quick scan of other sites, they consistently quote a higher value for people who have been training for years. So your mechanic should probably include some Athletics type skill to modify the lift capacity up.