This article is from the Amiga Networking FAQ, by Richard Norman with numerous contributions by others.
You need a 10baset transceiver called a TPAU (Twisted Pair Access Unit). The TPAU should have an RJ-45, and an AUI connection.
Set the jumper on the card for thick net. Use the thick network connector called an AUI and connect it to the TPAU's AUI connector and then connect the TPAU's RJ45 connector to your network. This setup requires two cables: one AUI, and one RJ-45.
For connecting the Thin net connection to twisted pair thin net instead of a co-ax thin net, you will need a ballun.
 
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