Bottom Bracket Spacers can be used for shimming a Tongsheng TSDZ2 or Bafang BBS02/HD to center it, or position the chainline. Sometimes, upon installation, the main reduction gear housing behind the chain ring will hit the bicycle's chain stay (which will also affect the TSDZ2 Torque Sensor reading), and you can place these behind it on the drive side to space it out a bit.
Offered in 1mm, 1.5mm, and 2.5mm sizes so you can get the perfect spacing down to 1mm tolerance.