I know less than nothing of these things - is it a salt as Roy says, or might it be like the Gladstone Bags - perhaps more ornamental than practicable - unfortunately, there's nothing on the original drawing to help.
To jump from a wheelbarrow to a colliery truck and maintain the same Rd. No. seems a bit tenuous to say the least - imagine saying to your gardener - sorry, you can't have the wheelbarrow today, you've got to push a colliery truck! - all on the basis that they both show gadroons and pimples, and the gadroons are barely gadroons anyway.
Anyway, since Henry Greener's original Registration 218710 is based on a wheelbarrow, here is the National Archives image of that Registration dated 20th September 1893. The National Archives Representations reference is BT 50/198.