Earlier this month, a video surfaced showing the incredible scratch resistance of the sapphire crystal display cover used in the stainless steel and Edition Apple Watches, and now another video claims to show the scratch resistance of the Ion-X glass display cover used in the Apple Watch Sport.

The video, from Lewis Hilsenteger of Unbox Therapy, uses Ion-X glass covers sourced from Sonny Dickson, who has acquired parts from various pre-release devices in the past. The glass covers in the video are said to be the same Ion-X covers used in the Apple Watch Sport.

Hilsenteger subjects the Ion-X glass to a key, a knife, steel wool, and several different sandpapers to try to damage it (skip to 2:30 to get to the scratch testing portion of the video).

While a key, a knife, and steel wool don't do any damage to the glass, Hilsenteger is able to scratch the glass quite significantly with sandpaper, suggesting that while it will stand up to day to day wear and tear, it's still possible to scratch the Ion-X glass under extreme conditions.

When the sapphire display cover of the more expensive watches is subjected to sandpaper, as in the video we saw earlier this month, it does not scratch due to the sapphire's greater hardness. Sapphire's scratch resistance is why it's used by many high-end watch manufacturers to protect watch faces as it's second only to diamond when it comes to scratch resistance on the Mohs scale.

Sapphire display covers are only offered in the higher-end Apple Watch and Apple Watch Edition models, presumably due to the high price of sapphire. The Apple Watch Sport, Apple's most affordable watch, has a lower price tag in part because it uses less expensive materials -- Ion-X glass instead of sapphire crystal and aluminum instead of stainless steel or gold.

The Apple Watch sport is priced more affordably than the other available Apple Watches, starting at a price of $349 compared to the $549 entry-level stainless steel watch and the $10,000 entry-level Edition watch.