ISO Lathe Toolholders

An ISO turning toolholder is a precision steel body that clamps a replaceable carbide insert and locates it at the correct cutting geometry for external turning, facing, profiling or chamfering operations on a lathe.

The holder fits into the tool post or turret of the lathe while the insert does the actual cutting. When the insert wears out it is simply indexed or replaced and the holder remains in the machine preserving setup repeatability.

ISO toolholders follow internationally standardised designations that describe the insert style, clamping method, approach angle, shank size and cutting direction.

ISO external turning toolholder part numbers follow a standardised coding system.

For example, PCLNR 2525 M12 breaks down as follows:

• P - Clamping method (P = lever lock / pin lock; C = top clamp + pin; M = top clamp only; S = screw clamp)

• C - Insert shape (C = 80° rhombic; D = 55° rhombic; S = square; T = triangular; V = 35° rhombic; W = trigon; K = 55° parallelogram; R = round)

• L - Clearance angle (N = 0°; A = 3°; B = 5°; C = 7°; P = 11°; G = 30°)

• N - Toolholder style (R = right-hand straight; L = left-hand straight; C = right-hand 75° offset; D = left-hand 75° offset; etc.)

• R - Cutting direction (R = right-hand; L = left-hand; N = neutral)

• 25 - Shank height in mm

• 25 - Shank width in mm

• M - Toolholder length designation (M, L, S, etc.)

• 12 - Insert size (inscribed circle in mm)

Decoding this designation allows you to identify compatible inserts and find equivalent holders across brands.

• Right-hand (R) - the most common! Insert faces to the right of the operator, feeding from right to left (towards the chuck/headstock). Suitable for the vast majority of external turning operations

• Left-hand (L) - mirror image of right-hand; feeds from left to right (away from the chuck). Used for back-facing, turning against a shoulder from the other side or on machines with reversed spindle rotation

• Neutral (N) - symmetric geometry allowing cutting in both directions making it useful for facing operations and on CNC turning centres where flexibility is important

Always confirm your lathe's spindle rotation and feed direction before specifying a handedness.

The clamping method (first letter of the designation) determines how the insert is held in the pocket:

• P - Lever Lock / Pin Lock - a lever grips the insert via its central hole, pulling it down and back against the pocket walls simultaneously. Excellent repeatability for fast insert changes. The most popular clamping method for general CNC turning

• C - Top Clamp + Pin - a top clamp bears down on the insert while a pin in the pocket hole prevents rotation. Good insert security so commonly used on conventional lathes and older CNC machines

• M -Top Clamp Only - a top clamp holds the insert without a locating pin. Simple and economical, most suitable for negative inserts without a central hole

• S - Screw Clamp - a central torx or hex screw passes through the insert hole directly into the holder. Very compact; commonly used for positive inserts and in boring bars where space is limited.

For CNC production work requiring frequent insert changes, lever lock (P) is generally preferred. For general-purpose use, top clamp (C or M) is reliable and simple.

We stock toolholder shanks from 8×8mm up to 40×40mm, covering the full range of lathe sizes:

• 8×8mm, 10×10mm — mini lathes, watchmaker's and instrument lathes, small precision turning

• 12×12mm — small bench lathes and CNC turning centres with compact turrets

• 16×16mm — light-duty conventional lathes and smaller CNC turning centres

• 20×20mm — the most common size for medium-sized conventional and CNC lathes

• 25×25mm — larger lathes and medium to heavy CNC turning centres; the standard for many industrial machines

• 32×25mm, 32×32mm — heavy-duty turning; large CNC turning centres and manual lathes with large tool posts

• 40×40mm — very large lathes for heavy turning and roughing applications

The shank must fit securely in your tool post or turret block without excessive play.

Check your machine's specification before ordering!

Our range covers all major ISO insert shapes, including:

• CN (80° rhombic) — the most popular all-round shape; excellent for general turning, facing, and profiling; good edge strength and versatility

• DN (55° rhombic) — more pointed geometry for profiling, angular faces, and undercutting; less edge strength than CN but better access

• TN (60° triangular) — three usable edges; economical and versatile for general turning and profiling

• SN (90° square) — four usable edges; ideal for roughing and heavy facing where edge strength and economy are the priority

• WN (80° trigon) — three wide-angle, very strong edges; preferred for heavy roughing and interrupted cuts

• VN / VB / VC (35° rhombic) — very sharp, pointed geometry for finishing, fine profiling, and tight corners

• RC / RN (round) — continuous cutting edge for profiling and copy turning

• KC (55° parallelogram / KNUX) — specialist geometry for specific angled cutting operations

The approach angle (also called the lead angle or entering angle) is the angle between the cutting edge and the feed direction. Common options in our range include:

• 0° (side cutting / facing) - produces low radial forces so is good for thin-walled components

• 45° lead angle - very common - distributes the cutting force between axial and radial directions, this reduces chip thickness and is versatile

• 75° - more axially biased so good for general turning with good access to shoulders

• 90° (square shoulder) - cuts true 90° shoulders - maximum radial force but needs a rigid setup

• 93° / 95° - used for back-turning and profiling operations - allows undercutting

Your choice of approach angle affects surface finish, chip load direction and whether you can cut true 90° shoulders.

• Negative rake holders - the insert pocket is angled so the insert sits at 0° or a negative rake angle. Used with negative inserts (e.g. CNMG, DNMG). The insert can often be used on both sides, doubling the usable edges. Strong, robust geometry for general machining on steel and cast iron

• Positive rake holders - the pocket tilts the insert to present a positive cutting angle, reducing cutting forces. Used with positive inserts (e.g. CCMT, DCMT). Better for stainless steel, aluminium & finishing operations where minimising cutting forces is important.

In principle, yes.

ISO standardisation means that an insert with the same shape, size, tolerance and fixing style should be interchangeable between brands.

However, subtle differences in pocket geometry and tolerance between brands can occasionally affect insert seating and precision.

For best results, check that the insert designation matches the holder specification exactly, particularly the size (IC) and tolerance class.

Our range covers a comprehensive set of insert size compatibility, including the most common sizes:

• Small (0602, 09T3, 0702, 0902) - for smaller holders (10×10mm to 16×16mm) and light finishing work

• Medium (1103, 1104, 1204, 1206, 11T3, 16T3) - the most widely used; compatible with 16×16mm to 25×25mm holders

• Large (1506, 1604, 1606, 1906, 2204, 2507, 2706) - for larger holders (25×25mm and above) and heavier roughing

Always cross-reference the insert size from your holder's designation before ordering inserts - the last two digits of the holder code indicate the insert inscribed circle in mm.