"is only used for" is correct and usable in written English.
It is typically used to explain the specific purpose or function of something. Example: "This type of hammer is only used for driving nails into wood."
The sequence number seq is only used for RTP packets.
This parameter is only used for HRC-I data.
Ta'leeli means preparation, but is only used for wedding preparations.
A solid probe is only used for calibration.
It is only used for the prediction of the heating value of the produced gas.
Note that they time is not recorded in the output file; it is only used for the reprojection.
Golden Bear Softball Field is only used for Cal Sport Club practices, summer camp activities, and special events.
It is only used for Rec Sports tennis lessons, Cal Tennis team practices, and Cal Tennis home dual match competitions.
This value is only used for DES keys; other keys use the preferred checksum type for those keys.
Which is used more often with non-restrictive clauses, and that is only used for restrictive clauses.
How, they ask, can gay people divorce for non-consummation without defining their dirty practices in law? (This is only used for Catholic annulments anyway).
