Focusing on the contact points between bolts and sockets. What are the advantages of ko-ken's Surface Drive, which thoroughly pursues surface contact?

When working with socket wrenches, sockets are essential. Sockets that come into contact with bolts and nuts have differences not only between 6-point (hexagonal) and 12-point (12-angled) but also between "line contact" and "surface contact." While surface contact is the mainstream for modern sockets, what are the advantages of surface contact? Here, we will focus on the contact area between sockets and bolts/nuts, and explain ko-ken's (Koken) proprietary Surface Drive, developed by a specialized socket manufacturer, as well as their unique spark plug wrenches.

Surface Contact Sockets Developed in Response to Requests from Aircraft Maintenance Sites

Whether to use a combination wrench or a socket wrench depends on the location of the bolt or nut. For flat surfaces, combination wrenches can be used, but when bolts or nuts are recessed due to steps, socket wrenches offer significantly better workability.

The biggest difference between spanners/combination wrenches and socket wrenches is whether the gripping part (handle) and the part that contacts the bolt or nut are integrated or separate. Spanners and combination wrenches have one grip for each size. Even if the sizes at both ends are different, such as 8x10 mm or 12x14 mm, a grip is needed for each wrench.

On the other hand, socket wrenches can be used with a single handle because the sockets are interchangeable. While handles and extension bars may be reconfigured for improved work efficiency, the characteristic of a socket wrench is that one handle can be used with multiple sockets.

Furthermore, compared to a spanner, which contacts two points out of the six vertices of a bolt, a socket that fits over the bolt and contacts all six points disperses rotational torque (load). If 2-point contact becomes 6-point contact, the contact area triples, meaning the load per point is reduced to one-third.

Applying a large torque with a spanner to a bolt or nut increases the risk of wear and stripping at the contact points due to excessive force. However, with a socket (similar to a combination wrench), the load is reduced to one-third, which mitigates damage.

However, when the socket contacts the vertices of the bolt or nut, the force applied to turn the socket concentrates on the vertices, making them prone to wear and increasing the risk of stripping due to play that develops with repeated attachment and detachment.

At this time, the bolt and socket make point contact, but since there is a height difference, the points connect to form a line, which is called "line contact."

To improve the situation where bolt and nut corners are increasingly damaged as tightening torque increases, "surface contact" was developed. This technology, or rather socket design, was conceived by Snap-on in the USA in response to demands from the aircraft maintenance field.

The biggest feature of surface contact is that the socket avoids contacting the corners of the bolt or nut. By avoiding the corners and contacting the six faces, stress is reduced compared to existing sockets that use line contact, and surface contact sockets allow for greater torque to be applied than before.

Snap-on patented this under the name "Flank Drive," and when the patent expired, tool manufacturers worldwide adopted surface contact, which has now become a common mechanism.

ko-ken's Surface Drive Significantly Improves Surface Contact Level

Surface sockets with a unique opening design that doesn't look like they are for hexagonal bolts or nuts.

When fitted onto a long nut, it's clear that the contact is made far from the hexagonal vertices. Since the vertices are not in contact at all, they can be used on bolts or nuts with rounded corners, and there's no worry about damaging the corners of delicate decorative nuts.

The strength of surface sockets lies in their ability to transmit torque without damaging seized bolts or nuts by maximizing the benefits of surface contact. They can be used with confidence on frames and suspension components tightened with high torque.

Surface contact mechanisms are now standard technology in sockets, and Koken, a specialized socket wrench manufacturer, offers products with "Flat Drive" for both 6-point and 12-point sockets.

Furthermore, "Surface Drive" is an evolution that further pursues the concept of surface contact, which is less likely to damage nut corners and can transmit strong torque.

In surface contact, the vertices of the hexagonal shape at the opening are rounded compared to line contact. It can be said that the faces connecting the vertices are arched to contact the six faces of the bolt or nut.

The internal shape of surface sockets that adopt Surface Drive is even more extreme, with no hexagonal vertices remaining and only six arches. It's almost concerning whether they will actually fit hexagonal bolts or nuts. However, this is precisely the shape that achieves thorough surface contact.

Since there are no corners to begin with, they naturally do not contact the corners of bolts or nuts. Furthermore, the unique arched shape contacts a wider area than Flat Drive, distributing strong torque. Additionally, they can turn bolts or nuts whose corners have become worn or deformed, causing conventional combination wrenches or sockets to slip.

They are also advantageous for delicate bolts and nuts, such as those with chrome plating or made of aluminum, as they apply less load to the corners, making them less likely to cause damage.

The only potential drawback is the shape, which is quite different from conventional 6-point sockets. However, just because contact occurs away from the corners does not mean there is play between the bolt/nut and the socket.

Incidentally, Koken's sockets also adopt the Flat Drive surface contact mechanism in the square drive portion that connects to the ratchet handle or extension bar. This has the advantage of dispersing the stress applied from the driving tool to the socket, increasing load capacity.

Surface sockets are about 20% more expensive than regular Flat Drive sockets, but they are undoubtedly reliable when performing tasks requiring high torque or when dealing with bolts and nuts with rounded corners on discontinued or classic vehicles.

差込角3/8インチのサーフェイスソケットのラインナップは5.5～24mmの20サイズ。その中から使用頻度の高いサイズをセットにしたのがRS3410M/12 The set includes 12 pieces: 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, and 19mm.

Surface sockets come in standard and deep lengths. The total length of a 10mm standard socket is 26mm, while a deep 10mm socket is 55mm long.

Unique Spark Plug Sockets Using Metal Clips and Brass Guides

コーケンが次世代のメカニックスタンダードと位置づけ、既存のラインナップよりさらにコンパクトさにこだわって開発したZ-EAL（ジール）シリーズのスパークプラグソケット3300CZ The drive size is 3/8 inch, and the sizes are 14, 16, 18, and 20.8mm.

On the two opposite faces of the opening, there are metal clips, and behind them, brass guides are inserted. The holes corresponding to the insulator diameter at the center of the guide work to suppress tilting without damaging the delicate insulators, which are made of ceramic.

Another product that showcases Koken's expertise as a specialized socket wrench manufacturer is the "Spark Plug Socket." Accessing spark plugs on modern motorcycles has become more challenging, and the process of removal and installation has increased compared to the past, yet spark plugs are components that need replacement according to mileage.

Spark plug sockets, used for removing and installing spark plugs, are broadly classified into three types based on how they hold the plug:

① Rubber Ring Type

This is a standard type that holds the ceramic part of the spark plug through the friction of a rubber ring or boot inside the socket. They are inexpensive, but their holding power may decrease over time as the rubber wears or hardens.

② Magnet Type

Magnets are incorporated near the opening, allowing the removal of loosened spark plugs by attracting the hexagonal screw part. This type is more resistant to aging than the rubber ring type, but there is a risk of cracking if the magnet strongly contacts the plug, and metal powder other than the plug may also be attracted.

③ Clip Type

Koken's clip-type spark plug socket falls into this category. Metal clips (leaf springs) hold two faces of the hexagonal screw part of the spark plug. It is free from problems like aging degradation of rubber or attraction of metal powder like magnets. Furthermore, it has a brass guide to prevent the spark plug from tilting inside the socket, allowing for straight insertion into the threaded hole even in engines where the screw part is deep within a spark plug hole.

For plugs that cannot be turned with a socket alone or a straight extension bar, Koken also offers spark plug sockets with a universal joint incorporated in the middle. With metal clips and brass guides integrated into the socket and drive portion, they have a slimmer profile than using a plug-in universal joint. Sizes are 14, 16, 18, and 20.8mm.

By incorporating a universal joint, the angle between the spark plug socket and the driving tool can be freely adjusted. This is beneficial for air-cooled engines, but its ease of use is even more apparent with water-cooled engines that have deep plug holes.

The inclusion of brass guides and metal clips increases the number of parts and machining processes, but the plug holding feel is exceptional, enabling reliable work. Koken's signature thin-wall design also reduces the outer diameter, allowing them to be used in the compact engine compartments of the latest motorcycles without snagging in the spark plug holes.

For Sunday mechanics who already own sockets and spark plug sockets, there may be no reason to purchase the same functionality again. However, the tools introduced here undoubtedly perform beyond conventional sockets.