One area where modern leaf springs differ greatly from their predecessors is in the various ways of combating internal friction and delivering a smooth, seamless increase in spring rate as the leaves make contact with each other. Older or heavy-duty packs may feature square-cut spring ends with no taper, but most modern light- and medium-duty springs feature Teflon or plastic anti-friction inserts along with tapered leaf edges. Diamond- or round-cut leaf ends also help reduce harshness and improve flex. The spring clamps are usually riveted in place and feature either high-movement bolt-on ends that allow a lot of leaf separation, or crimped ends which more closely hold the leafs together within the pack. Most off-roaders prefer the leaf separation afforded by the bolted clamps, but some say that the additional separation when the spring droops can induce fatigue and lead to snapped leafs.