What this op amp is and where it fits
The OP21GZ is a single-channel general-purpose operational amplifier in a ceramic 8-CERDIP package. It operates from 5 V to 30 V supply, draws 230 µA, and has 600 kHz bandwidth with 0.25 V/µs slew rate.
Key ratings and what they mean on the bench
The 0.25 V/µs slew rate limits large-signal response to roughly 40 kHz peak-to-peak at 10 V output swing — fine for audio, thermocouple amplifiers, and low-speed filters, but not for fast ADC drivers or video buffers. The 600 kHz small-signal bandwidth covers most sensor and control loops. Supply current of 230 µA per amplifier keeps the thermal budget low in multi-channel boards. Input offset of 40 µV is good enough to avoid external nulling in many precision circuits; if you need lower drift, the AD8622 (0.48 V/µs, 10 µV offset) is a surface-mount alternative, but it's a dual and requires reflow.
Package and handling in the field
The 8-CERDIP (0.300" wide, 7.62 mm pitch) is a standard through-hole footprint. It ships in bulk — loose tubes, not tape-and-reel — so you'll handle each part individually. Ceramic body is more rugged than plastic for repeated insertion/removal, but it's also RoHS non-compliant (leaded solder terminations). If your assembly line is RoHS-only, this part needs an exemption or a hand-solder station. Orientation is marked by pin 1 notch and a dot on the top; easy to get right without a magnifier.