Rod

A rod is not listed as a type of triangulation mark. However, it is commonly found on surface and buried blocks where it is used in place of a bolt. Records in the OSGB36 list do not distinguish between bolts and rods.

Typically, the rod protrudes by approx 0.5in above the block surface. A benchmark is sometimes cut into the block, for example Old Farm. The corresponding entry in the benchmark records may be annotated "TRIG BLOCK".

Copy Field

Examples of variations include:

cut on the top surface New Acres
square section Saltburn Grange
threaded Town End
dimpled Whinberry Naze

Damage may occur; either by vandalism or by the OS to indicate that the mark has been 'destroyed' and should not be used:

truncated Bryngates
bent West Hile

Figure 7.8 in The History of the Retriangulation of Great Britain ^[1] depicts a brass rod with the caption "Used as centre mark in concrete blocks at minor triangulation stations".