|
CUT MARK
By far the most common type. They were made and used from the 1800s to around 20 years ago.
They were chiselled into stone, brick or wood on all sorts of vertical structures and form a familiar horizontal levelling line with a three line arrow pointing towards it (usually upwards).
|
|
RIVET
Usually found on horizontal surfaces, these are cut marks with a small metal, domed brass rivet at the apex of the cut arrowhead marks.
|
|
FLUSH BRACKET
These are rectangular metal plates affixed to walls, buildings etc. They are about 6” x 3” in size and the location of most of them is known through Ordnance Survey (OS) records. If they are not affixed to a triangulation pillar (Trig Point or TP) they are often referred to as Non-Pillar Flush Brackets (NPFBs).
Each Flush Bracket (FB) has a unique serial number and there are several numbering types:
|
One to four figure number |
|
|
These FBs were the earliest and date from 1912-1921. Numbered from 1-3000.
|
|
S-prefix |
|
|
Introduced in the 1920s these are found on pillars and as NPFBs.
There are two sub-types – S below the number and S left of the number.
|
|
G-prefix |
|
|
First appeared in 1936.
Unlike S-series brackets below 1000 do not have leading zeroes.
Used extensively in Scotland and never found on triangulation pillars.
|
|
Five figure number |
|
|
These are effectively S-series brackets above S9999 where they ran out of room for the S
(S-below was discontinued as the S interfered with the measuring equipment).
|
|
|
BOLT
Used alongside the G-series of flush brackets these are placed where there is no convenient building or wall to provide a vertical surface on which to affix a flush bracket. They are domed, metal bolts about 1” (50-60mm) in diameter fixed to horizontal surfaces engrave with OSBM and the benchmark symbol.
|
|
PIVOT
Fairly rare, these are used on horizontal surfaces such as soft sandstone, where the insertion of a rivet would break away the stone. They consist of a small hole or depression cut to take a pivot, a steel ball bearing of 5/8” diameter (16mm). In use, the pivot is placed in the depression and the levelling staff held on top of the pivot.
|
