SC648NDR is a piezo buzzer from Mallory Sonalert with a 42.98mm diameter, panel mount, and voltage range of 12-48V DC. It produces sound pressure levels of 80 dB at 12V and 90 dB at 48V (2 feet), with a frequency of 2kHz.
The SC628 is a piezo buzzer from Mallory Sonalert Products with a nominal frequency of 2.9kHz and sound pressure level range of 79 to 90 dB(A). It operates from 6 to 28 VDC and is designed for panel mounting.
The Mallory Sonalert SCE048MA3DP3S is a piezo buzzer designed for panel mounting. It operates within a 28 to 48 VAC range and produces a sound level of 75 to 85 dB(A).