Introduction to Combination Wrenches

The mixture of a fixed spanner with a star spanner in a single two-end spanner with a single measure has given rise to mixed or combined spanners. Thus, for example, it is common to find flat-star or flat-rack combination wrenches of the same size to combine their advantages, i.e., the accessibility allowed by the star wrenches with the speed at which the fixed wrenches are operated.

Fixed, Flat or Open End Wrenches

Classic open-end wrenches are the simplest and consist of a single piece with a U-shaped opening which fits on the two opposite sides of a hexagonal or square head screw or nut. They often have two ends, with an opening of a different size at each end that combines consecutive figures or with a difference of two millimeters in large quantities.

Open end wrench

Generally, the ends are oriented at an angle of approximately 15 degrees to the longitudinal axis of the handle, allowing greater freedom of movement in confined spaces because the key can be turned.

The measurements and specifications of fixed keys comply with ISO 10102, DIN 3110, NF ISO 3318 and NF ISO 10102 standards, and the market generally has the following opening sizes, depending on the manufacturer:

  • Metric dimensions: 3.2 x 5.5 mm to 46 x 50 mm (e.g. 6 x 7, 10 x 11, 14 x 15, 27 x 29, 30 x 32 mm, etc.).
  • Dimensions in inches: 1/4 x 5/16 to 1 13/16 x 2 (e.g., 9/16 x 5/8, 11/16 x 3/4, 1 1/8 x 1 5/16 in., etc.).

Key sets are also available, either in a box, case, module or panel, which can hold between 5 and 15 keys each, depending on the manufacturer. Smaller key sizes, i.e., between 3.2 and 8 mm, are also marketed in a key ring type case containing between eight and ten tools.

The main drawback to the use of open-end wrenches is the need to make extensive angular travel (known as a recovery angle) to access the next face of the screw or nut. Also, by fitting only on two sides of the screw or nut there is a high risk of the wrench slipping, so the edges of the screw or bolt may be rounded.

Star Wrenches

The disadvantage pointed out for fixed keys is eliminated with star keys. These are ring-shaped open-end wrenches, the inside of which has a simple hexagonal configuration (six-sided) or with two crossed hexagons at 30° (twelve-sided) or a square shape (eight-sided). With the six-sided wrench, large tightening torques can be applied without the risk of slipping, as the wrench surrounds the bolt or nut and fits them perfectly.

Speaking of torques, check out our torque wrench buyers guide. We discuss the best torque wrenches out in the market right now.

The twelve-sided wrench has the advantage of holding the screw or nut in twelve different positions having a greater turning angle that allows the frequent change of the position of the wrench. It makes them very useful for assemblies challenging to access.

Star wrenches

Like fixed keys, star keys generally have two ends of different sizes, numbered in the same way as fixed keys, and are marketed in different designs. Let's look at the main ones.

Straight or flat star wrenches (ISO 10103, DIN 837 and NF ISO 10103 standards): these areas just described and also present a certain angle between the planes of the handle and the opening to avoid rubbing against the flat surface on which the screw is threaded.

Angled star wrenches (ISO 10104 and DIN 838 standards): their ends form a kind of elbow concerning the handle, and very useful in screws or nuts that are slightly sunk concerning a flat surface.

Half-moon star wrenches (ISO 3318 and NF ISO 3318 standards): the half-moon shape facilitates maneuvering on nuts that are inaccessible with a classic tool. The star configuration is usually 12-sided.

Ratchet or ratchet wrenches (ISO 1711-1 standard): the unique feature of these wrenches is that they only exert pressure in one direction of rotation (selectable by a small lever), leaving the rotation free in the opposite direction. They are extremely useful because they drastically reduce the recovery angle, particularly in places that are difficult to access or where there is little room for the key to move.

Open star wrenches or pipe fittings (DIN 3118 standard): these are straight, or flat star wrenches with an opening in the coupling opening. They are ideal for loosening and tightening hexagonal end fittings. Its main advantage is that they have a larger contact surface with the screw or nut, thus reducing the risk of rounding.

The most common metric measurements are: 7 x 9, 8 x 10, 11 x 13, 12 x 14 and 17 x 19 mm, and are mainly used in general industry and the different technical services dedicated to hydraulic, pneumatic and similar conduction.

Introduction to Combination Wrenches
Article Name
Introduction to Combination Wrenches
It is common to find flat-star or flat-rack combination wrenches of the same size to combine their advantages, i.e., the accessibility allowed by the star wrenches with the speed at which the fixed wrenches are operated.
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Jack Noelsson
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