This connector is a gray, 6 AWG with a length of 1.620 in (41,1 mm), a 0.200 in (5,1 mm) I.D. and a 0.344 in (8,8 mm) O.D.
The 3M™ Scotchlok™ Aluminum Connector 20001 is for use with copper or aluminum conductors. These aluminum connectors feature color coded end caps for identification. Contact aid provided in connector barrel is compatible with poly/EPR insulations.
Scotchlok Aluminum Compression Connectors - Data Sheet (PDF 37.2 K)