The metal case (Type B in DIN standards) provides an outer diameter (OD) that can be precisely machined for a tight interference fit with the housing bore. This construction is highly effective in applications where the seal needs to withstand a higher degree of radial force or when space constraints require a very thin cross-section. The rigidity prevents the seal from becoming eccentric or spinning in its groove, a common risk in high-speed machinery.

However, a drawback of the exposed metal design is its sensitivity to housing imperfections and potential issues with differential thermal expansion. If the seal (steel) is installed into a housing with a different coefficient of thermal expansion (like aluminum) and the temperature rises significantly, the housing may expand faster than the seal case, potentially leading to a gap and leakage around the OD. For applications with rougher bores or different housing materials, a rubber-covered OD oil seal is generally preferred.
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