What’s the fastest way to drive a nut 9″ down a rod of 3/8″ all-thread? Smart Tools’ Big Willy. They’ve come up with a line of hollow shank nut drivers specifically for 3/8″ threaded rod and only for 3/8″ nuts, since 3/8″ nuts usually require a 9/16″ socket.
They claim the Big Willy has a collet drive shank, which might mot mean much to you, but given that they show it chucked into a small impact driver, it looks to be just a standard 1/4″ hex shank. The driver is hollow for most of its length, except for an inch or so that the shank occupies. Be cautioned: Smart Tools made this tool for high-speed driving, not high torque applications, so don’t exceed 50ft lbs. with the driver.
The 3″ version of Big Willy runs about $11, the 6″ version — about $14, the 12″ version — about $20, or buy the full set of three for $40. Smart Tools claims they can manufacture the Big Willy in any length you require, so if you need something longer you can contact them.