Metal utensils,

their flat ones (i.e. utensils that do not have a receptacle)

and their receptacles (i.e. utensils that do have a receptacle)

are [susceptible to become] tamei.

If they [are tamei and then] break, they are tahor;

If one remakes them into a utensil

they return to their previous state of tumah (by rabbinical decree);

Rabban Shimon ben Gamliel says

not to any tumah,

only the tumah of death.

פרק יא משנה ב

Every metal utensil

that has a name of its own (and which does not need an additional qualifier - for example, a "knife" has a name of its own, as opposed to a "branch of a menorah" which requires the additional qualifier "of a menorah" to clearly identify what kind of branch is referred to)

is [susceptible to become] tamei,

except for the door,

and the door-bolt (a bolt or peg that is fastened to one side of the door and which can be slid upwards or downwards into a socket atop or below the door to lock it)

and the lock (which would be attached to a door)

and the socket that is under the door-pin (the hinges of the door of the mishnah are actually a pair of pins on one end of the door, one extending from the top the other from bottom of the door, and which went into corresponding cavities in the lintel above and the threshold below the door; the bottom cavity, which bore the weight of the door, was lined with a bronze cup to keep it from wearing away, which is the socket referred to here)

and the door-pin

and the beam (some say this is a beam in the roof of the house, others that it was across top of a doorway to prevent the door from swinging outwards)

and the pipe (some say that this particular pipe, others that it was a metal pipe-shaped lining around the cavity in which the bottom door-pin would rotate, and was used instead of a cup-shaped socket)

as they are [made to be attached] to the ground.