What the ESD Association says about wrist straps:
"Note: Metal expansion bracelet style wrist cuffs may trap moisture underneath and can be more effective for people with dry skin." [ESD Handbook TR20.20 section 220.127.116.11.3]
Per ESD Handbook TR20.20 section 18.104.22.168 Wrist Strap Checkers - “Wrist strap checkers have historically been the primary tool for testing the operation of the wrist strap system including, the wristband, grounding cord and most importantly, the electrical integrity of the contact between the wristband and the wearer. Wrist strap checkers measure the resistance of the entire system.”
NOTE: All bands have a 4mm snap stud. Complete wrist strap kits include an alligator clip. Wrist strap kits include an alligator clip for occasions when a grounded banana jack is not available. However, best industry practice is that ESD Ground Connections should be firm fitting connecting devices such as metallic crimps, snaps and banana plugs to be connected to designated ground points. Use of alligator clips is not recommended. (Ref: JEDEC Standard No. 625-A)
ANSI/ESD S20.20 Paragraph 22.214.171.124 Personnel Grounding Requirement "All personnel shall be bonded or electrically connected to ground or contrived ground when handling ESD sensitive items. When personnel are seated at ESD protective workstations, they shall be connected to the common point via a wrist strap system."
Click here for a Selection Chart on Desco Wrist Straps