Covered Bolts

Covered bolt at Redscar

Covered bolt at Fochno

Covered bolt at Therfield Heath

Lake District

A very small number of bolts have been found covered with a metal plate approx 12" square with the warning sign 'ORDNANCE / SURVEY / DO NOT / DISTURB' embossed on a raised circular disc at centre of the plate. To date (February 2023) all of these have been located within the southern portion of the Lake District National Park.

'Covered Bolt' is a trig baggers term; the corresponding OS term for the cover is 'Detector Plate'. This is mentioned, for example, in the Office File sketches for Ponsonby Fell and Kentmere Hall. In T:UK and OSGB36 the trig mark itself is listed as either a Bolt or Buried Block. As with Concrete Rings, the purpose of the cover is to aid in the detection of the trig when using a metal detector.

Trig Stations with a Covered Bolt

T:UK	Station name	Order	Computed	Block
TP17120	Gilpin Park	3	1950	SD47
TP8079	Lowick	2	1950	SD47
TP16492	Ponsonby Fell	2	1952	NY11
TP8081	Redscar	3	1950	SD47
TP13003	Top o' Selside	2	1950	SD47
TP7820	Wansfell Pike	2	1950	SD47
TP17121	Kentmere Hall	3	1950	SD47

Trig Stations where a Covered Bolt is suspected but not confirmed

T:UK	Station name	Order	Computed	Block	Notes
TP16495	Blake Fell	3	1952	NY11	Detector Plate 1'4" x 1'4" over Block

Others

A single instance of a cover with a different style has been found at Fochno in Dyfed. This in turn resembles the passive station sketch for Pegler's Tump. An unmarked iron plate covers the bolt at Therfield Heath.