The switch/solenoid mounts on top of the starter. As wrenchbender and glenn are both right there is some discrepency in parts termenalogy. NAPA has it listed as both a switch and a solenoid. If you need one the st33 will fit any of 6 cyl, use the side terminal if needed. The st11 will fit only the models that DO NOT need the side terminal. These links are for show you a picture. I have no affilation with the company.

http://www.napaonline.com/NOLPPSE/(S(s2xlh1uhcamdxt331s50dc45))/Results.aspx?Ntt=st33&Ntk=Keyword&N=0&Nty=1&D=st33&Dn=0&Dk=1&Dp=3

http://www.napaonline.com/NOLPPSE/(S(bgbzgauxh10ptybmabggq245))/Results.aspx?Ntt=st11&Ntk=Keyword&N=0&Nty=1&D=st11&Dn=0&Dk=1&Dp=3

They are so simple that replacement is rare. If age or wear has caused a loss of contact area they are avilable. The operation is the "wedge" when mashed moves about 3/8" to provide a contact bridge between the battery lug and starter lug there by powering the starter. Simple

Hope it helps
Brad


http://s320.photobucket.com/albums/nn343/brsdb3381/Tuesday_MY_56_Chevy/

56 3100 6 cyl