These are unwelded nickle plated O rings. The 7 mm has a 1/4" inside diameter.
7 mm np O ring----------4¢ each
12 mm np O ring----------5¢ each
16 mm np O ring----------6¢ each
19 mm np O ring----------8¢ each
25 mm np O ring----------10¢ each
When using unwelded O rings please be sure to close them tightly so they feel smooth to prevent accidents such as a nail, toe, beak or tongue getting caught in them.