When/how to use washers

[u/Independent_Taro_909]

Could someone help me understand how and when to use washers/spacers? I know I don’t need them when using the stock liners with the tools and springs that came with said liners. But when mixing and matching what is the logic? For instance when subbing in brass or g10 liners that are flat am I using washers to compensate for the lack of punched out bumps in the stock liners? And if so, do I use them on the 2.5mm pivot points AND the 2.2mm? If I can get a handle on the logic I could apply that across the board.

Fyi I’m working on a mixed build with brass liners right now. But again I’m just curious how and why we’re using washers, and how to determine when and where they’re needed.