Manhole cover (lid)Round, so it cannot drop through its own opening.
Manhole frameSome plans call it the ring; with the cover, the casting.
Manhole steps (rungs)Steel rungs coated in plastic; some sewer owners leave them out.
Eccentric cone (conical top)Its one upright side lines up with the steps.
Riser section (barrel)Stacked to reach the depth; 48 inches across inside is standard.
Base sectionFloor and lower wall, precast as one piece or poured in place.
Channel (invert channel)A U-shaped trough, as wide as the pipe, across the floor.
Grade rings (adjustment rings)Added or removed to set the frame level with the road.
Whole manhole, cut open 3
JointSealed with a rubber gasket, mastic or grout to stay watertight.
Bedding (base rock)A layer of crushed rock that the base is set on.
Invert (flow line)The lowest inside point of a pipe or channel.
Cover and chimney close-up 4
Finish grade (road surface)The finished surface that the cover is set flush with.
Pick holeA hooked tool goes in here to lift the cover.
ChimneyEverything between the top of the cone and the frame.
Chimney seal (infiltration barrier)A banded rubber sleeve that keeps water from seeping in here.
Floor from above 4
Inlet pipe (incoming pipe)Brings the flow in; one manhole can have several.
Outlet pipeCarries the flow out at the lowest flow line.
Bench (shelf)Slopes toward the channel so nothing is left standing on it.
Resilient connector (pipe boot)Rubber, clamped to the pipe to stop leaks at the wall.
How this list was compiled: Part names and every detail line were checked, for facts only and with nothing copied, against pages read on 2026-09-20. The standard: https://store.astm.org/c0478_c0478m-26.html (ASTM C478/C478M-26, Standard Specification for Circular Precast Reinforced Concrete Manhole Sections; the public scope names grade rings, flat slab tops, risers and conical tops, base sections, and steps and ladders). Oregon Department of Transportation standard drawings, the edition effective June 1 to November 30, 2026: https://www.oregon.gov/odot/Engineering/202601/RD338.pdf (sanitary sewer manhole: manhole cover and frame, adjustment rings, precast grade rings, precast conical top, a concentric cone allowed where steps are not required, precast risers, watertight joints sealed with grout, preformed plastic or a rubber ring, manhole steps, concrete bench sloped at least 2 inches to the foot, channel, manhole base, base rock, outlet pipe and lowest flow line, a standard section diameter of 48 inches, and the note that the number of pipes varies), https://www.oregon.gov/odot/Engineering/202601/RD336.pdf (manhole details: finish grade, precast conical top and precast flat slab top, the steps lined up with the cover and frame), https://www.oregon.gov/odot/Engineering/202601/RD344.pdf (manhole base section, cast in place or precast; channel shaped to the bottom half of the pipe), https://www.oregon.gov/odot/Engineering/202601/RD345.pdf (pipe to manhole connections: resilient connector, tracer wire) and https://www.oregon.gov/odot/Engineering/202601/RD356.pdf (manhole covers and frames: pickhole, manhole frame). Washington State Department of Transportation Standard Plan B-15.20-01, Manhole Type 1: https://wsdot.wa.gov/publications/fulltext/Standards/english/PDF/b15.20-01_e.pdf (manhole ring and cover, circular adjustment section, eccentric cone section, precast riser sections, steps or ladder, channel and shelf, integral base precast with riser, knockouts, diameters of 48, 54 and 60 inches). Iowa Statewide Urban Design and Specifications, Figure 6010.301 (Iowa DOT Standard Road Plan SW-301): https://intrans.iastate.edu/app/uploads/sites/15/2020/02/6010_301.pdf (casting, adjustment rings, precast top, joint sealant, precast riser sections, precast base with integral riser section, concrete fillet, lowest flowline, flexible pipe connection, Class I bedding material, infiltration barrier, steps where the depth is over 20 feet) and its Section 6010: https://intrans.iastate.edu/app/uploads/sites/15/2020/02/6010.pdf (adjustment rings also called grade rings; castings are the ring, cover, grate and extensions; the infiltration barrier is an internal or external chimney seal, a rubber sleeve held by bands; steps are steel encased in polypropylene and line up with the vertical side of the eccentric top; rubber O-ring or profile gasket, mastic and butyl wrap at the joints; the fillet is shaped as a smooth half pipe between the pipe inverts; incoming pipe and outlet pipe; an eccentric cone on sanitary sewer manholes unless told otherwise). For the words chimney and cone as defined terms, a seal maker's suggested specification: https://cretexseals.com/wp-content/uploads/2023/12/LSS-Inter-chim-seal-full-new-const-specs-8-18WEB.pdf (the chimney runs from the cone's top to the base of the manhole frame; the cone slopes upward and inward from the barrel). For the connector: https://store.astm.org/c0923_c0923m-20.html (ASTM C923/C923M-20, resilient connectors between reinforced concrete manhole structures, pipes and laterals, made to keep leakage between the pipe and the manhole small) and a maker's page that files the same product under manhole boot connectors: https://www.press-seal.com/products/psx-direct-drive/. A sewer inspection software maker's glossary, read as a second witness for the everyday trade words: https://blog.wincan.com/sewer-basics-parts-of-a-manhole-glossary (channel, invert, bench, barrel section, chimney, cone, cover and ring; the channel runs from the manhole inlet to the outlet; the bench turns flow back into the channel). Wikipedia, text only: https://en.wikipedia.org/wiki/Manhole_cover (pick holes take a hook tool; the cover sits on a metal base and the two are called castings; a round cover cannot fall through its circular opening), https://en.wikipedia.org/wiki/Manhole (also called a utility hole, maintenance hole or sewer hole), https://en.wikipedia.org/wiki/Sanitary_sewer (the manhole's concrete floor has channels) and https://en.wikipedia.org/wiki/Invert_level (the lowest inside level of a pipe, tunnel or trench). Licence: own work
The drawing: Our own original line drawing, made from our own geometry; nothing traced or copied. Read for accuracy against the public standard drawings of three state transport departments listed in this dataset's source, which were looked at and never traced, and this dataset's own researched part notes. Licence: own work
How it works
A sewer manhole is a stack of precast concrete pieces under an iron cover. This drawing cuts one open from the road down to the pipe, enlarges the top, and shows the floor from above, so each of the 19 names has a place.
Read the full guide
Manhole parts from the road down
The cover sits in the frame, flush with the finish grade. Grade rings under the frame bring it up to the road, and that stack is the chimney. The eccentric cone narrows the shaft, with its one upright side over the steps. Riser sections make the depth. The base section takes the pipes and rests on bedding.
Bench, channel or invert?
Look at the floor from above. The channel is the trough from the inlet pipe to the outlet pipe. The bench is the sloped floor on both sides of it. The invert is not a piece: it is the lowest inside point of a pipe or channel, the level a plan gives as a number.
Three rubber parts keep water out: the chimney seal at the top, a gasket in every joint, and a resilient connector around each pipe.
Questions and answers
What are the parts of a manhole called?
From the top: cover, frame, grade rings, cone, riser sections and base section, with steps on the wall. On the floor are the bench and the channel, which joins the inlet pipe to the outlet pipe. The drawing names 19 parts in all.
What is the bottom of a manhole called?
The bottom piece is the base section: a floor and the first height of wall, precast as one piece or poured in place. Its shaped floor has two parts, the channel that carries the flow and the bench on either side.
What is the chimney of a manhole?
The chimney is the adjustable height between the top of the cone and the base of the frame, built from stacked grade rings. A chimney seal, a banded rubber sleeve, lines it to keep water from seeping in around the rings.
What is the difference between an eccentric and a concentric cone?
An eccentric cone has one upright side, so the opening sits over the steps. A concentric cone slopes evenly all round, and Oregon's plan allows it where steps are not required. Some manholes have a flat slab top in place of a cone.
Which names does this drawing follow?
Names were checked on September 20, 2026 against ASTM C478 and the manhole plans of the Oregon, Washington State and Iowa transport departments. Where they differ (bench, shelf or fillet; frame, ring or casting), the most common is printed and typed answers accept the rest.