Anti-pull-out shank technology
A tool pulling out of the holder mid-cut scraps the part, can crash the spindle, and quietly caps how hard you'll ever push a tool. RobbJack's answer isn't a gimmick feature — it's how every shank is ground.
Why tools pull out
Pull-out comes from heavy axial loads overcoming the holder's grip on the shank. Three things quietly make it worse: a shank ground to a loose diameter tolerance only touches the bore on a few high spots; an out-of-round shank contacts even less; and a mirror-polished shank is simply too slick to hold. Push the tool hard enough — a full slot, a deep pocket, a big depth of cut — and it walks out of the holder.
The cost isn't just a broken tool. It's a scrapped part, a possible spindle crash, and a shop that learns to back the tool off “to be safe” — leaving real productivity on the table.
It's a complete process, not one feature
RobbJack's anti-pull-out shank comes from three things working together — the tolerance, the roundness, and the way the shank is finished. Any one alone helps; together they change how the tool holds.
h4 shank tolerance
The tightest diameter class in the industry — the shank fits the holder bore with almost no clearance, so the grip starts before the set screw or collet even closes.
Roundness under 0.000025″
Held to less than 25 millionths of an inch out-of-round. A truly round shank makes contact the full 360° around the bore, not just on a few high spots — that's where grip actually comes from.
Purpose-ground grip finish
The shank is ground — not polished — with a surface finish engineered to bite the holder. A mirror-polished shank looks nice and slips; ours is finished to hold.
Backed by consistency, tool to tool
A grip spec only matters if every tool meets it. Holding h4 and 25-millionth roundness on every shank, every lot, is a tolerance-and-process discipline — and it's the same discipline behind RobbJack's runout held under .0002″. The AL3 aluminum line ships with the anti-pull-out shank as standard, and RobbJack's ER solid extensions and Accuhold holders are ground to the same class, so the accuracy actually reaches the cut.
A note on Weldon flats — let us grind them
If you use a set-screw holder, the flat matters as much as the shank. RobbJack holds the flat width to under .001″ so the set screw locks against the sides of the flat, not just the bottom — and we grind Weldon flats (-FL) on our tools at no charge.
Grinding your own flat is the fastest way to undo the anti-pull-out shank: a flat that's slightly off in width, depth, or position lets the tool rock and pull out — or snaps it. Order it with the flat and it's right from the factory. More in the FAQ.
The numbers
- 150%
- up to — more gripping force in the holder
- 0.000025″
- shank roundness (25 millionths)
- h4
- shank tolerance — tightest in the industry
- 200+ HP
- full-slot aluminum cuts, held without pull-out
Keep going
Fighting tools that won't stay put?
Tell us the cut and the holder — we'll get the tool to hold, so you can run it the way it was meant to run.
Talk to an engineer