| btl | SolidWorks Sheet Metal Bend Table |
| btm | Microsoft BizTalk Map Data |
| btmsp | MALDI BioTyper Main Spectra File |
| btn | AutoPlay Media Studio Button Data |
| bto | Bryce Tree Object |
| btoa | Ascii85 Encoded Data |
| btp | Bend-Tech v3 Plate File |
| btpl | BluffTitler Playlist |
| btpx | Bend-Tech v6 Plate File |
| btr | AviSys Bird Watcher Database Index |
| btr | Btrieve Database |
| btr | Microsoft Frontpage Binary-Tree Index |
| bts | Blaise Specification |
| btsearch | BitTorrent Search Engine Data |
| btsk | HyperCard Button Task Data |
| btskey | BitTorrent Sync Data |
| btskin | BitTorrent Skin Data |
| btst | Norton SystemWorks Info Data |
| btsync | BitTorrent Sync Data |
| btt | ICQ Find Users Data |
| btt | Microsoft BizTalk Tracking Profile |
| bttx | Bend-Tech v6 Part File |
| btu | Diablo BTU Calculator and Reporting Data |
| btv | AppleTalk Desktop Database |
| btw | Bartender Format Data |
| btx | Bend-Tech v3 Part File |
| btx | DB/TextWorks Database Term and Word Index |
| btx | SEEDIS Index Data |
| btx | SmartWare Textfile Backup |
| btz | Helix Toolkit Compressed BT Data |
