These are the 5.5mm High Current Bullet Connectors from Castle Creations.
FEATURES: Gold plated Fits wire diameter up to 4mm Use 13 gauge to 10 gauge wires Up to 150A current
INCLUDES: Three sets of bullet connectors
REQUIRES: Solder and soldering iron - HCAR0776 and STAR2000
SPECS: Length: .66" (17mm) Diameter: .15" (4mm) inside (where the wire is soldered to) Diameter: .21" (5.5mm) outside