Smith & Tinker was an inventing firm based in the town of Evna.
Mr. Smith and Mr. Tinker were artistic inventors who created several fantastic machines. One of these is Tik-Tok the clockwork man, whom the firm sold to King Evoldo of Ev. Another is the iron giant which was made for the Nome King to keep folks from finding his underground palace.
The firm is now closed, due to the loss of both partners. Smith, the artist of the duo, painted a picture of a river that was so real that he fell in and drowned. Tinker, the inventor, made a ladder so tall that it reached to the moon. He climbed the ladder to the moon and once there pulled it up so no one could follow him. (Ozma of Oz)
Smith & Tinker are only briefly mentioned and never actually appear in the Oz books. (They are not the only such background characters in the Oz literature. Lurline and Hiergargo share the same status.) Tinker eventually surfaces in James Howe's Mister Tinker in Oz (where his full name Ezra P. Tinker is given) and Glenn Ingersoll's yet unpublished The Lost Queen of Oz. Smith reappears alive and well in the Oziana 1987 story "Button-Bright and the Knit-Wits of Oz" (where his full name Rejano Edison Smith is given).
Smith & Tinker clockwork resolves the primary conflict in John W. Kennedy's A Grown-Up in Oz.