The 2321 from KR Electronics (A Division of NIC) is a Low Pass RF Filter with Frequency DC to 0.3 kHz, Stopband Frequency 1 KHz, 3 dB Cutoff Frequency 0.3 kHz, Lower Rejection 40 dB@1 KHz, Upper Rejection 3 dB@1 KHz. Tags: Plug In. More details for 2321 can be seen below.