The M18 size of Bonded Sealing Washers is dimensioned by BS 4518. The table below gives the dimensional row from the standard, followed by the installation notes for this type.
M18 Dimensional Row (BS 4518)
Thread size
Inner diameter d1 (mm)
Outer diameter d2 (mm)
Thickness s (mm)
Seal material
Max temperature (deg C)
Reference standard
M18
18.3
26
2.0
NBR
120
BS 4518
Common Applications for M18 Bonded Sealing Washers
M18 Bonded Sealing Washers are commonly specified for high-load load-spreading on structural joints.
Mating Parts for M18
A M18 flat washer pairs with a M18 bolt/screw and matching M18 nut.
Technical Drawing
Customize the parameters below — every spec field is editable, and the drawing redraws to match the values you choose. Changing the size will snap the other fields to that size's standard values; you can then override any individual value.
Sends the selected values to the quote form below.
Request a Quote
The form below follows the current technical drawing configuration. Change the drawing values above and the request details update automatically.
Dimensions & Specifications (BS 4518)
Thread size
Inner diameter d1 (mm)
Outer diameter d2 (mm)
Thickness s (mm)
Seal material
Max temperature (deg C)
Reference standard
M4
4.1
8
1.0
NBR
120
BS 4518
M5
5.1
10
1.0
NBR
120
BS 4518
M6
6.1
12
1.5
NBR
120
BS 4518
M8
8.2
14
1.5
NBR
120
BS 4518
M10
10.2
16
1.5
NBR
120
BS 4518
M12
12.2
19
2.0
NBR
120
BS 4518
M14
14.2
21
2.0
NBR
120
BS 4518
M16
16.3
24
2.0
NBR
120
BS 4518
M18
18.3
26
2.0
NBR
120
BS 4518
M20
20.3
28
2.0
NBR
120
BS 4518
M22
22.3
30
2.0
NBR
120
BS 4518
M24
24.3
32
2.0
NBR
120
BS 4518
M27
27.4
36
2.5
NBR
120
BS 4518
M30
30.4
39
2.5
NBR
120
BS 4518
M33
33.5
43
2.5
NBR
120
BS 4518
M36
36.5
46
2.5
NBR
120
BS 4518
Materials & Grades
Select a material class to see the grades we supply it in. Each designation is listed with its ISO/EN, AISI/SAE, JIS and GB equivalents.
Third-party video, selected automatically for this topic. It is not produced by Engineering Hardware and is not a specification source — use the tables on this page for dimensional data.
Inside the plant
Manufactured in our own plant
This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided.
01
Cold heading
Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail.
Head dimensions and under-head radius checked at set-up and per shift.
02
Thread rolling
Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch.
Go / no-go ring gauges to ISO 965 tolerance class 6g.
03
Heat treatment
Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it.
Core hardness and tensile tested per lot to ISO 898-1.
04
Surface treatment
Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list.
Coating thickness and neutral salt spray hours to ISO 9227.
Frequently Asked Questions
Should M18 Bonded Sealing Washers be tightened by torque or by angle?
For critical structural joints at M18, angle-controlled or stretch-controlled tightening is more repeatable than pure torque — the friction scatter at large diameters can dominate the torque signal.
What grip range is typical for M18 structural bolts?
Grip ranges are highly application-dependent at M18. As a guide, choose a length that gives at least 1× the thread diameter engagement in the nut plus 2–3 thread pitches projecting.
Which washer dimensions matter most for M18?
For a flat washer, the outside diameter (the bearing surface) and the thickness control how the load is spread under the head and how much elastic preload is preserved. The inside diameter must clear the bolt body but not be so large that the head bears mostly on the washer's outer rim.
What is the coarse-thread pitch of M18 for Bonded Sealing Washers?
For M18 the standard coarse pitch is 2.5 mm — this is the value used for Bonded Sealing Washers.
How do I request a quotation?
Use the technical drawing on this page to pick the exact configuration, then submit it with the quote form. We respond within one business day.
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