OSBM Bolt: Waterston, Oil Refinery   

CUT MARK NBM PLATE TOP WKS TP SW SIDE AVENUE B NW SIDE JUNC RDS (56.5734m, 0.4m AGL, 3rd order, verified 1971) - what might "plate" mean?

Location
Grid reference: SM 9371 0548.
Landranger 157: St David's & Haverfordwest.
Landranger 158: Tenby & Pembroke.
Structure: Unknown.
Waypoint: OS2878.

Neighbouring Flush Brackets

G5100	Milford Haven, Pill Road 2.85km to the west.
G5099	Steynton, Hayguardhay Farm 3.05km to the northwest.
S7941	Pembroke Dock, Barracks 3.70km to the southeast.
G4919	West Popton Farm 3.81km to the southwest.
S7942	Pembroke Dock, Council Offices 4.15km to the southeast.

The nearest fundamental bench mark is Haverfordwest (1969), 10.70km to the north.