Laces, Metal Hardware and Zippers Functionally, the lacing system provides the last step in ensuring the foot is correctly seated and stable. Flat laces are not quite as convenient as round, but are far superior in regard to performance – particularly slippage. “Speed lace” metal hardware is most useful in the top 4 or 5 eyelets, after the bottom eyelets have been cinched in place using a “locking” eyelet. 5mm (tooth size) zippers from YKK® more than meet the burst strength requirement, and have good flexibility. The 10mm tooth is less flexible and prone to snapping under pressure.