All bolts, plate bolts and screws should always be tight, as well as
all pin block screws.  BUT, nose bolts should never be used to adjust
downbearing.  It is designed to support the cast iron plate at its normal
relieved position before stringing.  Before you decide to try adjusting
the downbearing by lowering down the nose bolt, make sure a replacement
plate is available!!  Downbearing should be adjusted before stringing by
varying the height of the bridge and/or the WHOLE plate.

Bob Lemon