The first keying part and second keying part are structurally identical.

The first keying part and second keying part are capable of allowing or refusing connection of said connector and said counterpart in dependence on the relative orientation of said first and second keying part.

The sealing system includes a keyed interface.

By providing identical first keying means of identical structure or shape, the manufacturing costs for these keying means are reduced, since only one type of keying means is manufactured.

Fool proofing is achieved by the corresponding designing sizes of the plug and the socket.

Mechanical coding is more reliable than visual coding, but more complex and more expensive to implement.

The cartridge comprises foolproofing means (31) engageable with second foolproofing means (32) connected to the predetermined holder (2) when the cartridge is mounted on the holder.

These foolproofing means are advantageously combined with preliminary support means for the housing.

Eliminating errors through mistake proofing (poka-yoke).

Each of the board holders includes a board insertion slot and a foolproof rib.

A and D-coded standard cables that are already in use can be retained.

A keying feature (15) is punched out of, and is integral to, the electrically-conductive element (6).

The foolproof ribs catch a portion of the board to prevent the board from being improperly inserted into the board insertion slot.

A replacement filter element is provided for such filtration sealing system, with the replacement filter element including a keyed interface.

The false fitting preventing projection 55 absorbs an impact applied from the outside, and serves as a cushioning member against at least the connector housing 13.