RCA "jacks" only come in one size. "Phone" style jacks come in two sizes, 1/8" (3.5 mm) and 1/4", and two types, TR and TRS (Tip-Ring, 2 contact areas, and Tip-Ring-Sleeve, 3 contact areas). Headphones use TRS (Right-Left-Ground). Pro-Audio uses both, TR (Unbalanced, for instruments like guitars, keyboards, etc.) and TRS (Balanced, used for interconnects, etc.).
Confused?

Anyway, 1/8"/3.5 mm TRS is probably what you were looking for.
WTT
Edit: I forget, There is a third type. Cell phones use a 2.5 mm version with 3 or 4 contact areas (R/L/Mic/Ground).
Edit 2: Here is the wikipedia version
Link