Impossible to install spark plugs!

IDK about 383s but the right plugs for SBMs are the ones that take a 5/8 thinwall plug socket. I think they are coded RN12YC/not sure; but they are 14mm,3/4 reach,copper,5/8s hex-drives.

Hah treed by 66fyssh
Edit;
RN12YC is wrong as noted below; the correct number being
RC12YC.
Now that I'm seeing it; I think my plug code had a J in it.