Yup, Mark, you are absolutely correct. Pulled out my thread gauges and checked some of my stands. Mine are 1/4-24 with and without the captive nut. 1/4-24 was evidently fairly common before World War II. Harley-Davidson actually used this size; restorers need those taps and dies.
slingerfan!
So, you're saying that the thread with the captive nut is also 1/4-24? My stands that use captive nuts are 1/4-20.
-Mark