SWTX

SWTX (Server / Workstation Technology eXtended) is a proprietary computer case and motherboard form factor used by Supermicro primarily for 4-socket servers.

Longer but narrower than WTX, SWTX motherboards are not compatible with (E)ATX cases because of their size and mounting scheme. Likewise, ATX motherboards are not compatible with SWTX cases.

Dimensions: from 16 xx to 18 xx. Most SWTX boards seem to be in the middle of this range, around 16.48 xx.