Andre,
I reckon it could be done with the bottom rail in the upper position of the pentaclip.
BUT the saddle is only held by the bottom rail which on my twin rail saddles measure 5.75/5.82 mm chromed/painted and my single rail saddles all measure 7mm. So a lower strength when using just the lower rail.
I did not fancy my wife being on the 'bleeding edge' of technology, certainly not in such a crucial area, if the saddle rail failed.
Sadly the pentaclip guys have missed an opportunity to offer a 'brooks twin rail' pentaclip with the alloy side pieces cast to have the right spacing and size for the twin rail saddles. It looks eminently feasible.
I will be interested to hear how you get on if you try it.
Julian.
Thanks, Julian. I've been looking at the Pentaclip on and off for years, but didn't know anyone reliable who had one to ask until you came along. I don't fancy being on the bleeding edge of technology either (!), so I think I'll give it a miss. Those Brooks clips are unbelievably crude and nasty, but they'll just have to soldier on.
If the rails on the single-rail and the double-rail saddles were the same, I might have tried it but, with your measurements in hand, I've now concluded that it is extremely likely that those two rails are part of the suspension rather than merely fixing points, and that they're scaled for both rails to be clamped for either purpose, holding the saddle on the bike (and your backside off a crude apple corer) and isolating your spine from the road.
Thank you so much for the initiative of the measurements, and for going to the trouble.