So, are they the same?
The simple answer is “No, shim washers are not the same as flat washers, even though they look the same. They may share the exact same internal diameter (ID), outer diameter (OD) and thickness”. So, A Cow Is Not A Cow?
Bad analogy and confusion aside, shim washers and flat washers are inherently different in their purpose and tolerances. Here are three differences that set shim washers apart from flat washers.
Purpose And Usage
They serve a different purpose in life. While flat washers are used for fastening, load distribution and surface protection, shim washers are used for gap alignment. Flat washers are usually used together with screws, bolts or nuts. While shim washers can be used in the same way, they can be slotted into threaded screws or axles to carry out their job.
Tolerances
Based on DIN125A standard, flat washers are produced with nominal dimensions with no tolerance values given. Our flat washers are supplied with the understanding that the thickness variance will range from 0 to 0.2mm. For example, an M3 flat washer will have thickness ranging from 0.4mm to 0.6mm, even in the same batch!
Shim washers are produced to close tolerances, usually up to 0.2mm for ID and OD, and as small as +/-0.02mm for thickness.
In short, shim washers are more precise than flat washers because they have to be. During gap alignment or leveling, minor differences in thickness and diameters must be taken into account for fear of misalignment.
Available Thickness
Flat washers usually have a single thickness based on a given ID and OD. For example, an M3 flat washer with ID 3.2mm and OD 6mm will have thickness 0.4mm. If you are lucky (or not), you might find some with 0.5mm in the same batch. Not reassuring? Not to worry, being used for fastening, the thickness of flat washers is usually not a focal point.
With the same ID and OD, reputable distributors (ahem) will usually provide shim washers with a range of thickness that you can choose from.
Being used for gap alignment, shim washers are produced in a range of thicknesses. It is not unusual to find shim washers available in up to ten thicknesses such as 0.01mm, 0.02mm, 0.03mm, 0.05mm, 0.10mm, 0.15mm, 0.20mm, 0.30mm, 0.50mm and 1mm.
