This is an Apple Ethernet transceiver. It's an adapter for connecting older Macintosh computers with AAUI-15 ports to a 10BASE-T Ethernet LAN using an Ethernet cable. I think it's a very rare item nowadays. It says "MADE IN USA". Apple Desktop Bus (ADB) connected peripheral. - Model: MK437 - Country of Manufacture: USA - Connection Type: Apple Desktop Bus (ADB) - Port: RJ-11 - Compatibility: Apple products 【Please Note!!】Please confirm the following. I purchased this used over 15 years ago to connect a thin PowerMac 6100 to a network. The 6100 broke down shortly after, and I kept it stored away as I was deciding whether to use it with another Mac, but then all my Macs died. It was working at the time, but I cannot guarantee that it works now. Please purchase only if you understand the above. Instant purchase OK. Thank you for looking.