Many ways can retain parallels in a vise set-up. Normally the idea is they are supported during part changes, plus keeping swarf from getting underneath.
I commonly retain them with an arched spring, using steel tape found on palletized shipments.
Common sizes are 1/2", 3/4" and 1" wide, add a couple leaves when more pressure is required.
Notice the trick for sawn material, to avoid the burr at the lower edges.
Narrower parallels on the outside give plenty of burr clearance. Saves a lot of time in multiple parts, first off by saving at least one de-burr on each.