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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:

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".


  1. The History of the Retriangulation of Great Britain 1935-1962, p.225, 'Types of Station Marks'