Well these are not all mano's that's for sure, some are though. I have no idea of all the uses possible Jon. I believe some of these were used to wear grooves in hammers and axes, others used as pecking stones.
You need to take a closer look at the center photo first row .dont i see obvious wear around the band of most of those? a color change from the natural skin? i pick up stones like those by the pocketful on the beach...same size and shape...but no sign of wear like those look to have.