Re: Correct spark plug for 1924 Model D Elto Ruddertwin Home › Forum › Ask A Member › Correct spark plug for 1924 Model D Elto Ruddertwin › Re: Correct spark plug for 1924 Model D Elto Ruddertwin garry-in-michiganLifetime MemberReplies: 3583Topics: 31 April 3, 2018 at 6:02 pm #73411 The AC C-87 aligns perfectly with the Champion C-7, which I believe was the original spark plug used. . . 😀