Flame Boss 300 using an adapter from a BBQ Guru?

I can't comment on a guru adapter or PBC. I do agree that the flame Boss universal adapter is a tad on the cheap side. It doesn't fit snugly but my Shirley is forgiving enough to where it doesn't matter much. I'll standby for someone more knowledgeable

All Guru adapters are about 1-1/8" ID. The Flame Boss fan nozzle is about 3/4" OD. The FB fan nozzle has a ball detent to keep it from falling out of even their own adapter because it does not fit properly. If you want your FB fan to fit properly without air gaps that will cause your fire to overshoot you are on your own. Take your fan to a machine shop and have them make something that the fan will fit.

Yes this does suck for something that costs well over $300.

My FB was the 100 model.
The Guru will run the FB fan. The pin plugs are the same sizes. I made my own adapters for both the FB and Guru.
Like mentioned, the FB fan will not stay inside the Guru adapter. But, I did find an "O" ring, 3/16 wall thickness (if I remember right) that after removing the ball detent wasn't to bad of a seal. But you had to have the fan horizontal into a 90 degree elbow. So the fan sits/fits down into the elbow. If that makes sense.

I use the Guru 25cfm Pitbull fan because I have a larger smoker. I was using the 20 cfm fan from my Auber. If you are going to stay with the Flame Boss fan you can go to Home Depot and get a threaded adapter and just drill it out. The Flame Boss is awesome!