With competition-level LiPo batteries mostly available with either 4mm or 5mm plugs, mix and matching different brands with various sizes plugs might a traditional challenge. Arrowmax had tested the rescue by developing a 5mm to 4mm down-sizing layer. Different and also other comparable products in the marketplace now, the layer functions placing towards the 5mm plug on LiPo and efficiently changing it to 4mm. No soldering and very convenient to maneuver from pack to pack. You'll keep your asking cable and ESC connection with similar 4mm plugs but still to use LiPo with 5mm conncetion. They come 24K silver plated for maximum conductivity.