My bike had a dealer fittted saddle when I bought it. I removed it recently while cleaning and was surprise to see it held on with 5mm bolts and thin washers behind the nuts which were dished and almost pulled through the eye of the spring mount.
There is a lug on the frame through which the bolt passed. The lug would take an 8mm bolt but the hole in the toolbox was about 7.5mm, so I opened it up to 8mm. I fitted an 8mm bolt (both sides) with sturdy washer and nyloc nut. The saddle feels "more attached" to the bike and more comfortable. I guess it could have failed in time with perhaps serious consequences, hence the heads up.