This may seem very rudimentary, so forgive me. I have a Manfrotto 3299 QR plate and mount, but the thread size is much larger than the piece on my tripod to where I can mount it. Are there any thread converters out there that go from smaller to larger?
The only way that this seems to work is if I remove the entire pan/tilt head and attach the piece, but then the tripod would only work on truly level surfaces...
If I understand what you're saying, your tripod has a 1/4"-20 screw coming out of the top, and your QR base has a 3/8"-16 hole. The B&H links you provided appear to confirm this problem.