You identify an insert (also called press insert or jaw insert) by two things: the profile of your fitting and the pipe size in mm. Pick your brand in the checker, or look up your profile + size below.
An insert is the interchangeable part that clicks into the master jaw. The master jaw sits in your press tool; the insert gives the fitting the correct press contour. Which insert you need can be read from two things:
Examples: M15 = M profile, 15 mm · TH16 = TH profile, 16 mm · U16 = U profile, 16 mm · V15 = V profile, 15 mm.

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View the sets →The size is the outside diameter of the pipe/fitting. These are the common sizes:
| Material | Profile | Common sizes (mm) |
|---|---|---|
| Multilayer / plastic | TH U UP | 16 · 20 · 25 · 32 · 40 |
| Copper · stainless steel · steel | M V | 12 · 15 · 18 · 22 · 28 · 35 |
The size is almost always printed on the fitting or the packaging. In doubt between two sizes? Measure the outside diameter of the pipe.
For one size you need one insert (one per press size). If you press several sizes or materials, you are better off with a complete set: 1 master jaw + 19 inserts in the profiles TH, V, U and M, with UP as an option. With it you press virtually every common fitting, whatever the brand, instead of buying separate inserts for each job.
Not directly: the insert fits into the master jaw, and the master jaw is chosen by the kN class of your machine: 32, 19 or 15 kN. Don't know which class your press tool has? Pick your machine in the press jaw checker and you'll see straight away which master jaw (and therefore which inserts) fit.