Published 13 July 2026 at 04:46
A standard V-block has a simple V-shaped groove on its top surface. Cylindrical workpieces are placed in the groove and held in place via TWO LINE contacts (the two sides of the V-groove). This is the standard choice for most round-stock tasks — I wrote about magnetic V-blocks for sk-se previously.
But for certain measurements, a single V-groove is not enough. If you need to verify a cylinder’s ROUNDNESS in BOTH horizontal directions without moving the workpiece, the 2-line contact does NOT provide stable positioning — the cylinder can roll or tilt. This is where the X-block comes in.
The X-block’s crossed groove
An X-block has TWO V-grooves CROSSED at 90° to each other. From above it looks like an “X” or a cross. A cylinder placed at the center of the crossing point is held stably by FOUR CONTACT points (one per V-groove arm):
- The V-groove in the X direction: 2 line contacts along the length of the cylinder (as with a standard V-block).
- The V-groove in the Y direction (perpendicular to X): 2 additional line contacts across the cylinder.
Net result: the cylinder is stabilized in BOTH horizontal planes. No risk of rolling or tilting.
When 4-point contact is critical
Roundness measurement: When a cylinder needs to be verified for radial runout, it must be rotated STABLY in the measurement setup. The X-block holds the cylinder centered while the operator turns it for dial indicator readings.
Multi-point measurement on the same cylinder: When several dimensions need to be measured (diameter at different axial positions, concentricity of multiple segments) without repositioning the workpiece.
Precision milling of round-stock ends: When a mill needs to machine the end of a workpiece, the cylinder must be held absolutely still — the X-block provides that 4-point stability.
Rolling process QC: Verifying rolled cast cylinders for roundness after manufacturing.
Standard V-block vs. X-block: selection criteria
V-block: Simpler, cheaper, smaller. The standard for most round-stock tasks where stability in one direction is enough.
X-block: Larger, heavier, more expensive. For applications requiring FULL 4-point stability.
When in doubt: start with a V-block. Upgrade to an X-block only if the V-block proves insufficient for the specific application.
Class 1 precision
DIN 876/1 for X-blocks defines:
- Flatness of the surfaces: ≤ 6 μm over 100 mm.
- Parallelism between base and top surface: ≤ 8 μm.
- Perpendicularity of the V-grooves to the base: ≤ 5 μm over 100 mm.
For workshop use where ±10 μm precision on workpiece positioning is acceptable, class 1 is sufficient. For calibration lab work, class 0 is used (double the precision, 3-5× the price).
Cast iron material
X-blocks are made of cast iron — the same material as granite surface plates (I wrote about those for m-dk previously) or triangular straightedges (t-dk). Reason: dimensional stability over decades, vibration damping, robustness.
Weight: 6 kg per pair (3 kg per block). Heavy enough to stand firmly without sliding on a granite surface plate, compact enough to move by hand.
Ø 8-90 mm capacity
The geometry of the crossed groove determines the range of cylinders it can hold:
- Ø 8 mm: smallest cylinder — sits at the very bottom of the cross intersection.
- Ø 90 mm: largest — sits across the entire top of the cross.
For larger cylinders (Ø 100+ mm), a larger X-block is needed. This 120×100 mm size is the standard mid-range.
Applications
Roundness QC on precision cylinders: Motor shafts, hydraulic cylinders, rolling mill rollers.
Piston and piston ring measurement: Diameter, roundness, taper.
Milling of round-stock ends: Keyways, snap-ring grooves.
Roller and roll verification: After grinding, to verify roundness.
Toolmaker’s work: Precision manufacturing of cylindrical components.
Quality control lab: Reference setup for cylinder testing.
What you get for your money
Schut X-blocks in pairs (2 pieces), cast iron material, 120 × 100 × 60 mm per block, crossed V-groove for Ø 8-90 mm cylinders, class 1 precision tolerance per DIN 876/1, hardened ground reference surfaces, approx. 6 kg total weight per pair, ECONOMY LINE build quality. DKK 2,216.
A standard tool for roundness QC and 4-point stabilization of cylindrical workpieces in workshop measurement. A complement to the standard V-block (which provides 2-line contact). For most round-stock tasks, a simple V-block is sufficient; the X-block is for specific applications where full 4-point stability is critical.
Read more: X-block in pairs Ø8-90 mm in the shop →
