I should refine what I wrote in my post above. When I used the term "more rigid", I meant only that the insert is, technically speaking, held more securely than a Top Notch style insert.
In the Top Notch system, there is a groove molded into the top side of the insert. The groove (or "Notch" as it refers to) is at about a 45º angle. The pocket in the tool holder is almost square and flat (most people don't realize there's actually about a 3º inclination angle) and nothing in the pocket secures the bottom of the insert. The tool holder's top clamp pulls the insert back into the pocket as it pushes down.
The Iscar tool shown, as well as the myriad other choices from other makers, has V-grooves on both the top and the bottom of the insert, and corresponding features on the holder make for a very secure, bi-directional grip on the insert. With certain groove/turn type of inserts, you can easily do some fairly heavy duty turning with the tool. When doing that, the holder's "support blade" carrying the insert is engineered to flex a bit so that the insert isn't rubbing the whole face as you traverse from left-to-right or right-to-left. That flex, though slight, is there and is why most other makers of similar tools do not offer threading inserts in their double-ended grooving/parting tool systems.
By contrast, the Top Notch is only good for cutting pressures from the 90º quadrant opposite the holder's insert pocket nesting corner. The makes them good for compound infeed threading and suitable for straight-in grooving. I use the Top Notch for threads coarser than 8 threads per inch and for snap ring, O-ring, and thread relief grooving. I might also use the Top Notch threading inserts for any thread that I don't yet own the proper pitch-specific lay-down 16ER/IR insert. There are now available a limited range of cresting (full form) threading inserts for Top Notch, but they are harder to find and probably the same money or more than the relatively easy-to-find 16ER/IR styles.
I'll try and get some photos of both styles. This is another case of a picture is worth 1000 words.
In the Top Notch system, there is a groove molded into the top side of the insert. The groove (or "Notch" as it refers to) is at about a 45º angle. The pocket in the tool holder is almost square and flat (most people don't realize there's actually about a 3º inclination angle) and nothing in the pocket secures the bottom of the insert. The tool holder's top clamp pulls the insert back into the pocket as it pushes down.
The Iscar tool shown, as well as the myriad other choices from other makers, has V-grooves on both the top and the bottom of the insert, and corresponding features on the holder make for a very secure, bi-directional grip on the insert. With certain groove/turn type of inserts, you can easily do some fairly heavy duty turning with the tool. When doing that, the holder's "support blade" carrying the insert is engineered to flex a bit so that the insert isn't rubbing the whole face as you traverse from left-to-right or right-to-left. That flex, though slight, is there and is why most other makers of similar tools do not offer threading inserts in their double-ended grooving/parting tool systems.
By contrast, the Top Notch is only good for cutting pressures from the 90º quadrant opposite the holder's insert pocket nesting corner. The makes them good for compound infeed threading and suitable for straight-in grooving. I use the Top Notch for threads coarser than 8 threads per inch and for snap ring, O-ring, and thread relief grooving. I might also use the Top Notch threading inserts for any thread that I don't yet own the proper pitch-specific lay-down 16ER/IR insert. There are now available a limited range of cresting (full form) threading inserts for Top Notch, but they are harder to find and probably the same money or more than the relatively easy-to-find 16ER/IR styles.
I'll try and get some photos of both styles. This is another case of a picture is worth 1000 words.