The present invention relates to an indexable milling insert and a corresponding basic body, intended for use in milling tools of small diameters, foremost in rotary shank-end mills for the machining of metallic workpieces. The invention also relates to a milling tool having indexable milling inserts detachably mounted in a basic body. The milling insert, according to the invention, is mounted in the basic body without fastening members, which considerably facilitates the mounting of the milling inserts for the operator who should handle the milling tool. According to the invention, an interface is created between milling inserts and basic body that guarantees that the milling insert is kept in place in the correct position during the milling operation, without a fastening member needing to be used. The milling insert is fitted tangentially obliquely down into the body from the side by means of a key and is locked in all directions using a lock means of the milling insert and the basic body, respectively. The lock means consists of locking surfaces and coupling means, and the interface created by the lock means provides the milling insert a satisfactory stability.