The are 64mm :-) Or a pair of RB20 TB's they are 60mm. There was even a car in the Hyper Rev mag that used dual RB20 TB's. After that mag was released (1997) lots of shops went to the RB TB's. Just glue them on and go!! j/k Have them jimmy-rigged on there and run a splitter for two throttle cables. The hold on the plentum behind the TB's will need to be bored up. It is only like 52mm.