One Piece Units

Cover frame adjusting units are reinforced 65mm deep units which can be used in place of engineering bricks to adjust the ductile or cast iron covers and frames to the required level and are kitemarked to BS EN1917:2002/BS5911-3:2010

Adjusting units are available for the following access sizes (mm):
600 x 600, 675 x 675, 750 x 600

600 x 600 Eccentric/Corbel units have an eccentric opening which is used in conjunction with a 750 x 600 cover slab opening.

The advantages of adjusting units are:
  • They can be quickly and easily installed by semi-skilled labour
  • There are fewer joints which reduce the likelihood of infiltration
  • All concrete manhole units can be ordered from one source
  • There is a reduced risk of on site damage and pilferage

Two Piece Units

Two piece adjusting units are now available with a 600 x 600 or a 675 x 675 opening.

Two piece adjusting units offer the following advantages:
  • Each section weighs less than 25kg enabling one man to handle the units and comply with manual handling regulations.
  • No requirement for bricklayers due to ease of installation.
  • Quicker to install than brickwork.

Scottish Water seating slab (Lothian Slab)

Special seating slabs 1125 x 1125 x 150mm thick, to comply with Scottish Water Services Specification are available with access sizes 600 x 600, 675 x 675, 750 x 600 and 750 x 750.

It is the customers responsibility to check that the proposed cover and frame flange is fully supported by the chosen adjusting system as flange sizes vary between manufacturing.

For sales into England and Wales please call 01179 814500 or email

For sales into Scotland please call 01698 386922 or email


Click on the images below to view the image gallery.

  • Do you recommend surrounding pre-cast concrete manholes with in-situ concrete?

    Concrete surrounds to manholes are not always necessary in the majority of situations. However if the sewer is to be adopted, this may be a requirement.

  • Do you supply certificates of conformity for your standard products?

    No – they are not required as our standard products are certified under the BS ‘Kitemark’ system – certification can be viewed here.

  • What is the standard position of the access opening in cover slabs?

    The standard access position is 150mm in from the chamber wall below (measured from centre of nearest access edge to inside of chamber wall below). Other positions/access sizes/multiple access slabs can be made to order.

Got a question?

To find out more about Adjusting Units/Seating Rings, please call our Sales Team or fill out the enquiry form and we’ll get back to you within 24 hours.

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