220Ω Resistor

The 220-ohm resistor is a two-terminal fixed passive that sets or limits current by Ohm's law (V = I x R). At this 6.3mm by 2.5mm axial body size it is typically a 1/4W (0.25W) carbon film part, matching Yageo's CFR-25 family. 220 ohms is a standard E24 (and E12/E6) preferred value, so it is stocked everywhere and shows up in nearly every hobby kit.

It is non-polarized: neither lead has a defined polarity, so it can be soldered or inserted in either orientation. On a 4-band carbon film part the value reads Red-Red-Brown-Gold, where gold marks the common +/-5% tolerance (so an in-spec part measures roughly 209 to 231 ohms). Precision metal film versions of the same value are offered at +/-1%.

Its signature job is limiting current to an LED. From a 5V logic pin driving a ~2V red LED, 220 ohms passes about 13.6mA; from 3.3V the same LED sees about 5.9mA, both safely inside a typical LED's rating. The CFR-25 body is rated to a 250V maximum working voltage, but the binding limit in practice is power: dissipation is V-squared / R, so a 1/4W part is fully loaded near 7.4V across it.