Straight Slot Bits (SL)

Bits under the straight slot (SL).

A straight slot (SL) is a simple recess for a flat screwdriver. It looks like a slot made in the head of a screw or self-tapping screw. A distinctive feature of the straight slot is the small contact area of the tool with the fastener (when the bit or screwdriver rotates, its edges touch the inner surface of the slot only at two points). Therefore, the flat slot SL (or Slot) is absolutely not suitable for tightening fasteners with a large torque. Despite its simplicity and versatility, nowadays it is used less and less (mostly only for tasks that do not require much tightening effort).

Splined bits are found in almost every set of replaceable nozzles, including the most low-cost ones. In the marking, they are indicated by the letters SL and numbers indicating the width of the blade in millimetres. In everyday life, it is useful to have at least two or three bits wide from SL4 to SL8 (and flat screwdrivers of small and large sizes are usually needed only by specialists).

Cross-slot bits (PH, PZ)

Bits for a cross-shaped slot (PH).

Fasteners with a cross slot and the corresponding screwdrivers for it appeared in the 30s of the last century, when the characteristics of screws with a flat slot ceased to suit the engineering industry. The cross-shaped slot in the "head" of the screw or self-tapping screw allows you to precisely centre the tool, and the four contact planes between the phillips screwdriver or bat and the inner surface of the slot ensure the transmission of increased torque. Therefore, fasteners with cross-shaped slots can be tightened with much greater effort, without fear of "licking" the head or damaging the tool.

There are about a dozen varieties of cruciform slots, but in fact only two are used: Phillips (PH) and Pozidriv (PZ).

Cross-slot bits (PZ).

The PH cross slot has been designed specifically for pneumatic and electric screwdrivers. It looks like a slot in the form of a "cross" with a slight thickening in the centre. The corresponding bits and screwdrivers are marked with the letters PH and numbers indicating the size: 0000, 000, 00, 0, 1, 2, 3 and 4. Most often, the sets include bits ranging in size from PH1 to PH3, and the rest may be needed only for highly specialized tasks.

The PZ cross slot is visually different from the PH. On the surface of the fastener head with a Pozidriv slot, additional "whiskers" are noticeable, and on the PZ bits there are corresponding "ribs". These additional elements allow you to transmit even more torque than the PH slot. On screwdrivers and bits of this type, the letters PZ and the numerical designation of the size are indicated: from 0 to 5. The most necessary type in the household is the PZ2 bit (almost all Pozidriv type screws that you may encounter at home or at a construction site will be of this size).

Despite the external similarity, the cross nozzles of different standards are not completely interchangeable. The fact is that the faces of the Phillips slot are slightly beveled at a slight angle, and the inner surfaces of the Pozidriv standard cross slot are vertical. Because of this feature, the PH type tool has a tendency to push out of the slot at high torque, and the PZ nozzles are devoid of this disadvantage. Therefore, although the PH bits can be used to tighten the PZ fastener (but not vice versa), it is better, nevertheless, to use the appropriate tool for each type of fastener.

Bits for square and hex slots (SQ, Hex)

Bits for the square slot (SQ).

Four- and six-sided slots appeared as an alternative to cruciform ones when it became necessary to increase the torque when tightening the screws without increasing the size of their heads.

SQ (Square) bits under the Robertson slot have a tip of the working part in the form of a square profile. The numbers indicating the size (from 0 to 4) are indicated in their marking. Screws and screws with square slots are rare, but you may need SQ bits if you are engaged in car repair (especially Canadian production) or carpentry. The most useful square bit sizes are SQ2 and SQ3.

Hexagon slot bits (Hex).

Hex (Hexagon, Allen) bits under the Allen slot have a working part in the form of a regular hexagon. The corresponding fasteners are used very widely, especially in the furniture industry. Even ordinary plastic windows are regulated using hexagons (but special elongated keys are usually used for this). Bits of this type are indicated by the letter H and numbers indicating the size (the distance between opposite faces). In everyday life, the most useful and in-demand tool is the size from H3 to H6. There are also "vandal-proof" HH bits (Hex Hole, Hex Tamper Resistant or Hex Tamper Proof) with a hole in the centre.

Bits for the star-shaped slot (T, TX, TH)

Bits under the star-shaped slot (T).

Fasteners with star-shaped slots and tools for working with them entered circulation more than 50 years ago, when complex equipment and industrial robots appeared on the assembly lines of automotive enterprises. The shape in the form of a six-pointed asterisk significantly increases the contact area between the bat and the slot. This allows you to tighten the fasteners with a very large force without damaging the head and working faces of the tool. There is almost no tendency to push the bits out of the slot, so the screwdriver or screwdriver does not need to be pressed in the axial direction during operation.

Nowadays, fasteners with "stars" can be found anywhere — from laptops to cars. There are several different standards, but the most common are the usual Torx slot (a recess in the form of an asterisk with six rays) and its "vandal-proof" version of Torx Security (there is a small protruding pin in the exact middle of the slot, to work with such fasteners you need a bit with an appropriate hole in size).

Bits under the star-shaped slot (TH).

Torx bits are marked with the letter T (some manufacturers have the letters TX) and numbers indicating the size: from T1 to T100. The most popular sizes are T10, T15, T20, T25 and T30. Small bits (from T2 to T4) are needed only by those who repair computer equipment and consumer electronics. The marking of the Torx Security bits (they can also be called Torx Hole or Torx Tamper Resistant) indicates the designation TH (sometimes TR), and their size range is completely identical to the Torx nozzles. The Torx Security tool can be used to work with Torx fasteners (but not vice versa).

Bits for Apple Technology (P)

Bits for Apple Technology (P)

Screwdrivers and bits designed for twisting and unscrewing screws with slots in the form of a five-pointed star with rounded edges became popular a little more than 10 years ago thanks to Apple. It was then that the "vandal-proof" fasteners of the Pentalobe standard began to be used to assemble MacBook laptops, iPhone smartphones and iPod players. Tool manufacturers instantly set up the production of screwdrivers and attachments for fasteners of this rare standard, and now it is not difficult to buy bits for disassembling Apple equipment.

In tool catalogs, Pentalobe bits are indicated by the letter P and numbers indicating the standard size. Those who repair electronics may need tools ranging in size from P1 to P6. Please note that some nozzle manufacturers use other letter designations (TS or PL), and the size range of such bits does not correspond to the values adopted by Apple (for example, P2 is TS1, and P5 is TS4). Also, Pentalobe bits should not be confused with the five-beam version of the Torx slot, because these are completely different standards, and they are incompatible with each other.

Rare and Special bits

In addition to bits and attachments necessary for working with widespread flat, cross and star-shaped slots, there are also numerous special bits that are used for twisting and unscrewing rare types of fasteners.

Spline bits.

The Spline bits have a working part in the form of a twelve-pointed star with 60-degree angles at the apex of each beam. This design allows you to transmit a very large torque. Therefore, "stars" with 12 beams are used where the maximum possible tightening force is required (for example, in the automotive industry for engine assembly). The marking of the Spline bits indicates the size of the fastener they are designed to work with (from M5 to M20). Twelve-pointed stars should not be confused with "double hexagons" and "triple squares" (XZN). Despite the fact that they all have the same number of beams, they are incompatible with each other due to the different geometry of the profile.

Tri-Wing bits.

Tri-Wing bits are nozzles with three blades, each of which is slightly offset relative to the centre of the slot. The advantage of this design is the transmission of torque without axial pressure. Previously, fasteners with Tri-Wing slots were used only in the aerospace industry, but in recent years many manufacturers of household appliances have used it as an "anti-vandal" protection from users. Therefore, you may need three-bladed bits from TW0 to TW5 for assembly and disassembly of some types of equipment and electronics (and large nozzles from TW6 to TW15 will be useful only if you are engaged in aircraft maintenance). Tri-Point (or Y-Type) nozzles can sometimes be confused with Tri-Wing bits — they also have three working faces, but the blades are not offset relative to the slot.

Torq bits.

Torq bits (Torq-Set) are four—bladed cross nozzles with an offset centre. This slot is extremely rare (mainly in aviation), but can sometimes be used as an "anti-vandal" solution. The Torq bits are marked with the letters TQ and a numeric size designation (from 0 to 10). Some tool manufacturers use the letters TS.

Triangle bits.

Triangle bits are nozzles with a working profile in the form of a regular triangle. Screws with triangular slots are used infrequently, but sometimes they are used to block access to the engine or battery compartment of household appliances. Triangular bits can be denoted by the letters TR or TA. The most "running" sizes are TR2 and TR3.

Clutch bits.

Clutch bits are necessary for tightening and unscrewing screws with slots in the form of "butterflies" or "hourglasses". Fasteners of this type are rarely used in Europe, but in the USA they are much more common. Clutch bits are marked with the letter C and numbers indicating the size: conventional (like C1 or C3) or in inches (for example, C1/8" or C5/32").

Spanner bits.

Spanner bits are fork wrenches with two pins. Screws of this standard are used to protect against unauthorized access. They are used to attach elevator panels or block access to electrical panels in trains and public places. The marking of the Spanner bits includes the letters SP and numbers indicating the standard size (from SP1 to SP10). This tool has many names. Manufacturers can designate such bits with the words U-type, Snake-Eyes, Two-Hole, Twin-Hole or Pig-Nose.

Bits for hooks.

Bits for hooks are quite rare attachments. They are not found in every set. There is no single standard for bits for twisting hooks, so they look different from different manufacturers. Such a bit can be similar to the letter Y with a groove covering the surface of the hook, or made in the form of a cylinder with a transverse slot.

Hexagonal End heads

Hexagonal end heads.

Hexagon heads are the most common type of end attachments. Their profile provides good coverage of bolts and nuts. The size range and marking are exactly the same as for ordinary wrenches. The depth of the standard head is at least 25 mm, and the elongated ones have a working part length of 50 mm. For small heads, the landing square is usually 1/4" in size (but as the working size of the tool increases, the counter part also grows: 3/8", 1/2", 3/4" and 1").

Twelve-sided end heads

Twelve-sided end heads.

The twelve-sided heads, as the name implies, have a profile with 12 working faces. They differ in more accurate and convenient positioning on the fastener, because the 12-sided nozzle can be rearranged with a rotation of only 30 ° (unlike 60 ° for 6-sided ones). But there is also a drawback: due to the reduced contact area of the heads with 12 faces, they are more prone to "licking" bolts and nuts, especially if we are talking about small fasteners. The dimensional grid of the twelve-sided end heads is completely identical to the hexagonal nozzles.

Surface / Super Lock End Heads

Surface / Super Lock end heads.

The Surface or Super Lock heads correspond to the hexagonal nozzles in the size range, but differ from them in the shape of the profile. Their inner surfaces are not straight, but slightly convex. Therefore, when rotating, the head presses not on the very corner of the fastener face, but a little closer to the middle. This design feature allows you to use Super Lock heads to tighten and unscrew slightly "licked" or deformed bolts and nuts.

Torx End Heads

Torx end heads.

Torx heads (sometimes called E-profile heads) are similar to the bits of the same name. The inner surface of this tool has the form of a six-pointed asterisk. With the help of Torx heads, it is impossible to twist ordinary hexagonal fasteners, but they are perfect for tightening and unscrewing bolts and nuts with an E-profile, which are increasingly found in the construction of cars and some other types of equipment these days.

Spline End Heads

Spline end heads.

Spline heads are the most versatile type of end attachments. They have alternating straight and rounded faces, which (if the head is correctly sized) provide good contact with various types of fasteners. Having at your disposal a set of Spline attachments, you will be able to twist ordinary hexagonal bolts and nuts (and not only metric standard, but also inch), as well as Torx fasteners and even three-, four- and twelve-sided fasteners.