After Geofkkait chimed in I decided to call Alfred and ended up speaking with his lovely wife Betty who confirmed after a 5 minute hold, she needed to look it up on SR literature, that the SR 20's are indeed directional with the the "0" end being inserted into the fuse holder. She also said the Blacks are less so and try it and see it which way sounds better to you. I know, wishy washy. But experience with these fuses bear it out. I also found this but may be may be nothing new to you old hands,
In my experience nearly all fuses are directional including SR Quantum Fuses. I recommend you try them in one component at at time and experiment with directionality. You should immediately notice a preference for one direction or the other. If a component has more than one fuse use a DVM (Digital Volt Meter) to determine direction of current in the circuit. Once you know the direction of current in each fuse holder place all fuses in like direction paying attention to have the letters on the SR Quantum Fuses all in the same direction either reading in the direction of signal flow, or against. Next switch direction and the correct match to your component should be readily apparent. There are just too many variables for me to make a blanket recommendation for all components when such a simple and definitive test is available.
As to having to take a reviewers word for it (or not,) regarding which fuse to try / buy you have the option to audition SR Quantum Fuses for 30 days in your system with a full refund of the cost of the fuse should you elect to go a different way. Our 30-day no risk audition policy takes the guess work out of trying SR Quantum Fuses and is offered because I am certain we make the best sounding fuses in the world.
Yours in music,
Ted Denney III
Lead Designer, Synergistic Research Inc.