I mean same SMD package size. This diode is for reverse battery protection. If you can read electronic circuit look here Texas Avenger "TA" Driver series - Triple channel + Bistro or Narsil + Clicky or E-switch - The Ultimate open source driver!
The FW21Pro must use similar design I see from your picture. In multimeter diode test RED (positive) probe must be connected to diode Anode and negative (Black) probe to Cathode. Multimeter in that connection must measure actual voltage drop across diode, which for schottky diode is about 0,3-0,4V. When you replace probes directions i.e. RED to Cathode and Black to Anode diode must not conduct. Schottky diode compared to regular diode have lower forward voltage drop.
If you don’t know how diode work see that good video
What Is a Diode? - YouTube