Heading 4105 covers skins that have been tanned or crusted but not further prepared — essentially intermediate tannery outputs. Heading 4112 covers sheep and lamb leather that has been further processed after tanning or crusting (e.g., buffed, dyed, plated, or otherwise finished), making it ready for direct use in manufacturing articles.

Wool removal is a defining requirement of heading 4105 — all goods here must be without wool on. Skins that retain wool are classified elsewhere in the tariff schedule (typically under raw or dressed fur skin provisions). The tanning or crusting process itself does not determine wool-on versus wool-off status; that is a separate preparation step.