The CD74HCT21M is a dual 4-input AND gate from the 74HCT logic family, in a 14-SOIC surface-mount package. The 74HCT series uses TTL-compatible input thresholds (0.8V low, 2V high) while running on a 5V CMOS rail, making it a direct drop-in for 5V TTL legacy designs or mixed-logic boards that need CMOS output drive with TTL-level signaling.
The 27ns max propagation delay at 4.5V and 50pF load is the timing spec to close in your bus-margin analysis — it's the worst-case delay across temperature and voltage, so your setup/hold budget needs to accommodate it. Quiescent current maxes at 2 µA, which keeps the power rail draw negligible in standby or battery-backed sections.