This question should really be in the FAQ's. It gets asked at least once by each new member.

"Tank" is the X Marks term for a hand-sewn, 8 yard, at least 13 oz., Worsted Wool Traditional kilt.

It was coined about two years ago by a former member to denote the durability of those most prized and sought after of kilts. They are so durable and practical that many are in their second or even third generation of owners.