I think the 3700 might be the Super GP3300's that some teams had (but did not use) at the worlds. The IFMAR illegal GP3300's were 23mm in diameter and weighed over the 63g limit. Most were 64-67g.
What I run: Schumacher Mi5/Associated RC10R5.1/Associated RC12R5.2/Futaba/HobbyWing/Team EA Motorsports/BSR Racing
Where I run: Florida Indoor R/C Complex/Thunder Racing/Florida On Road State Series