"SQ" in part number designates Square Flange design with holes drilled in corners.
"RC" in part number designates Square Flange with severely rounded corners (no holes).
"A" in part number machined from aluminum - "B" from brass.
All boots machined from aluminum ("ST" - Straight)("AN" - Angled).
"BOX" fittings are computer mounted with one boot needed.
"LINE" fittings are wire hook-ups with boots at both ends

These 1808 series fittings are "Line Fittings" (as shown on the right of upper photo) in 1/12 scale and are used as quick disconnects for "Inline Wiring"  where two exit boots are required. These are the largest of the two sizes available.