Lox-On chimney fits burner models 12, 21, 21c, A, B, C, 23, which were made from 1950's until the end of the 20th century. Base of chimney has small bumps that engage with tabs on burner top. Aladdin's exclusive borosilicate glass is shatter resistant and can withstand immense heat. All chimneys carefully inspected and are free of bubbles and other defects. It's the finest lamp chimney available, made from the same kind of glass they use in laboratories! 12-1/2"H, 2-5/8"OD base. How to Install: Set chimney into gallery, then twist gently to lock into place.Caution: If overtightened, chimney will break in use.