Hardness testing of small screws and bolts.

Any metallurgical lab could assist you in sample preparation. If you have large volume sample preparation requirements, then you would probably need meatllographic sample preparation equipment like diamond wheel cut off saw and a number of abrasive wheels and compounds to achive a good sample without contributing additional hardness.

A sample run through a lab probably be more advisable to refine procedure and equipment.

If the parts are a reasonable size then a small hand held portable hardness tester with a built-in magnifying glass and light is also available from PTC instruments. It may be also be available from Techni-Tools, Edmund Scientic, or through a Test equpment suppliers list annually published by "Quality" magazine. Hope this helps.