3,967. Examples of Interpositions

Hilchos Klei HaMikdash 10:7

A kohein must be careful when donning his garments that nothing – not even dust or a living insect – is between his skin and the garments. Air should not be allowed to enter between the kohein and his garment while serving, causing the garment to billow away from his skin. The kohein may not insert his hand into his tunic [i.e., in the style of the famous Napoleon pose], nor remove his hair from the garment, nor may a thread be left hanging from the garment. If one of these things happens, his service remains valid.

Hilchos Klei HaMikdash 10:8

But what if a kohein wrapped a cloth on his skin in a place that his garments don’t cover, such as on a finger or on his heel? If the cloth is three fingerbreadths by three fingerbreadths (approximately 2.25”x2.25”), it is considered an interposition and disqualifies the service; smaller than that is not considered an interposition. Since a small belt is considered a garment in its own right, it invalidates the service even if it doesn’t meet that minimum size.