The number engraved on the wrench or socket is the size of the opposite side, that is, the S value of the specification of the threaded connection fastener found in the mechanical design manual. Many people may not understand this parameter and think that it is the diameter of the thread. As a result, the selected wrench does not match the screw/bolt/nut.

À présent Torc Stark will show you how to choose the right wrench or socket according to the bolt specification. First, take a look at the size comparison table of metric external hexagon bolts and metric internal hexagon bolt wrenches.

Comparison table of the opposite side of metric hexagon bolts and socket (Torx) wrenches:

No.Hexagon Bolt SpecificationsThe opposite side of the corresponding wrench or socket

Comparison table of dimensions of metric Allen Bolts and Allen wrenches:

No.Specifications of Hexagon Socket BoltsThe opposite side of the corresponding wrench or socket

The screw size corresponds to the four faces of the Allen wrench. In order to let everyone distinguish the corresponding size of the screw and the Allen wrench, as well as the size of the tap to be used for the hole to be drilled,

Here are some experiences for your reference:
Calculation of the bottom hole for tapping:
Brittle materials (cast iron, bronze, etc.): drilling diameter d0=d (thread outer diameter)-1.1p (thread pitch);
Plastic material (steel, copper, etc.): drilling diameter d0=d (thread outer diameter)-p (thread pitch)
The open-end wrench used in the outer hexagon is more accurate to correspond to the hexagon nut because there are hexagon head bolts and small hexagon head bolts.

Commonly used open-end wrench specifications are: 7, 8, 10, 14, 17, 19, 22, 24, 27, 30, 32, 36, 41, 46, 55, 65;

The corresponding thread specifications are: M4, M5, M6, M8, M10, M12, M14, M16, M18, M20, M22, M24, M27, M30, M36, M42

The minimum size of the full set of Allen wrenches is 3, and the corresponding relationship is S3=M4, S4=M5, S5=M6, S6=M8, S8=M10, S10=M12, S12=M14-M16, S14=M18-M20, S17=M22-M24, S19=M27-M30, S24=M36, S27=M42.

Calculation method for the diameter of tapping the bottom hole of the front thread: for brittle materials, follow the basic size – 1.0826 thread pitch, and for plastic materials, follow the basic thread size – thread pitch + 0.1. Brittle materials are in pure cutting state when tapping, and the size of the bottom hole is the diameter of the thread bottom circle. When the plastic material is plastically deformed when the material is subjected to force during tapping, the material will move to the small diameter of the thread, so the bottom hole should be appropriately enlarged. . For threaded holes below M6, regardless of material properties, the basic size – pitch is uniform. The size of the drill hole is generally the major diameter D of the bolt minus the pitch.

A Wrench Data Sheet is attached with each series of TorcStark hydraulic wrenches. You can find out the applicable bolts for each model under each series according to this table. For example, there are torques in the table, the length, width and height of the square rotor or the diameter of the inner hexagon, etc. Of course, TorcStark also provides hollow sockets et square sockets to be combined with hydraulic wrenches to work on various sizes of bolts.


For bolts of different specifications, you need to know the data of the thread, and then find the appropriate wrench or socket according to the data of the bolt (The number engraved on the wrench or socket is the size of the opposite side, that is, the S value of the specification of the threaded fastener ). A suitable wrench will greatly improve work efficiency and ensure personal safety. Of course, if you come across a bolt with an odd specification, please feel free to contact TorcStark. With decades of bolting experience, TorcStark will provide you with the perfect bolting solution.