Holdfasts are very useful to me in my shop but they can be troublesome at times. I own the Gramercy holdfasts and for the money they are the best option out there. But, sometimes they just don't grab as well as I would like. In addition, I find myself placing sacrificial pieces between the metal tip and my nice work piece to avoid dents, specially in softwoods. For a while now I have been using a scrap of thick leather between the holdfast and my wood and found it to be best. The leather does two things. It protects the work piece and because the leather is thick and compresses it gives me better grip. So, about 6 months ago I glued leather to the tips of two of my holdfasts and have been very pleasantly surprised with how well they grip my work without damaging anything.
All you need for this is some thick leather. You don't need a lot so call saddle shops or anywhere horses may be. They will either know where you can get some thick vegtable tanned leather (also called veg tan leather) or may have some scraps just laying around that you can pick up for free. Worse case look on the internet and search for vegtable tanned leather, in a thick ounce. Leather thickness is measured in ounces, yeah it's weird, just find some 7-8 oz leather. Don't use sued leather, it is to thin and not thick enough to compress and give you the protection or grip that you are looking for. You will also need a good glue like gorilla glue or something that can bind leather and steel, maybe an epoxy, but I have never used anything but gorilla glue for this myself. And a clamp and knife.
The process is quit simple. Just cut some small pieces, spread the glue, spray with water, clamp, and let sit for a few hours for the glue to dry. Make sure the holdfast tips are clean before you glue to them. If needed use a little sandpaper to sand the pad clean of any oil or grime. Also, use just enough glue for the area, gorilla glue expands a lot and can cause some very messy results. You don't want to come back and find your holdfast is now glued to your clamp and anything else close by.
Once the glue is dry just cut the extra off with a knife. And your done.
I plan on doing this same thing to all the metal pipe clamps I own. Not that I won't still use cauls when needed, but I think the leather will add projection when I do not.
**Added Note....... The leather, in my opinion, should be mounted with the smooth side out. The smoother side will hold up better over time. If something gets on the leather it can be removed with a little light sanding.