Coming from Arrowmax are 5mm to 4mm reducer sleeves that allow to use LiPo batteries equipped with 5mm tubes, with standard 4mm bullet-type connectors. The latest breed of LiPo batteries often comes with 5mm connector tubes whereas the former industry standard was 4mm, making it necessary to have different charging cables and even power connectors at hand when using both types of batteries. The reducer sleeves will kick in here as they are inserted in the 5mm tubes, effectively creating a 4mm hole that is usable with all standard 4mm bullet type connectors. The sleeves come as pairs, they are 24K gold-plated and are easily swapped between battery packs.