Bolts with an M42 designation is among the largest bolts that are available. The requirements for M42 bolts are quite specific. When utilizing M42 bolts, engineers and fabricator must consider the effect that the thread pitch and the grade of the bolt will have on the joints over an extended period of time.
The bolt specifications provides information regarding the standard pitch for M42 bolts. Engineers utilize the bolt specifications to ensure that the dimensions of the bolts will be able to meet the requirements of heavy structural projects in which they are to be utilized. There are four common thread pitches for M42 bolts.
Simple Guide to M42 Bolts
These four thread pitches are provided to accommodate for the different levels of precision that is required in different applications of the M42 bolts. Coarse threads are easier to install than fine threads. Coarse threads are also more forgiving of the way in which the M42 bolts is handled during installation.
Fine threads allow for the bolt to have a higher level of preload capability. Fine threads also provide more resistance against vibration of the bolt. The 2 mm thread pitch is often used in applications that are exposed to constant cyclic loading.
A 2 mm thread pitch allow for the bolts to have a larger stress area. A larger stress area allows the bolts to be able to handle more load. However, using smaller thread pitch obtains larger stress areas, which can make installation of the M42 bolts slower.
The grade of the M42 bolt is just as important as its pitch. Grade 8.8 M42 bolts are able to handle most structural work. However, most specifications require that 10.9 grade or 12.9 grade M42 bolts be utilized.
High-grade M42 bolts allow for fewer M42 bolts to be utilized in a structure. This is due to the fact that high-grade M42 bolts has higher strength than lower-grade M42 bolts. Using fewer M42 bolts allow for the structure to have less weight than if the number of bolts were higher.
Using fewer M42 bolts also reduces the fabrication time required to install the structure. However, using fewer M42 bolts means that each bolt will be subjected to more load than if there were more bolts in the structure. The torque that is applied to the M42 bolts will also affect how the bolts are utilized in the structure.
If the bolts are to be lubricated, there will be less torque that is required to install the bolts compared to when the M42 bolts are to be dry. If the M42 bolts are installed without adjusting the torque requirements for lubrication, the bolts may either under-torqued, or the bolts may yield with excessive force during installation. The dimensions of the M42 bolt head and the M42 nut are also important elements of the M42 bolt.
The 65 mm wrench size is used for M42 bolts. This size of wrench provide for a large enough bearing surface for the bolt. Heavy hex nuts have larger dimensions for height and width.
The larger size of these nuts ensures that there is more surface area in which the nuts will distribute the forces created by the M42 bolts. If the M42 nuts are to be hot-dip galvanized, then the extra material used for the nuts and M42 bolt head will allow for more zinc coating. The added thickness of the coating to the threads of the M42 bolts means that the M42 bolt must have a 6g tolerance class.
This tolerance class for the M42 bolt will ensure that the M42 nut will be able to fit onto the M42 bolt even after the application of the zinc coating. The installation process for M42 bolts is notably different than that of smaller sizes of bolts. The tap drill size must be larger for M42 bolts.
Cutting speeds must be slower for M42 bolts. If the M42 bolts are to be utilized in blind holes, sequences of taper, plug, and bottoming tools must be used. The bolts must be installed using calibrated torque wrench.
The M42 bolts may require amounts of torque as high as 2000 Nm. Such a high amount of force requires calibrated M42 bolts to be installed. The procedures for installing these bolts must be documented in advance so that the bolts can be correctly installed.
Bolts with an M42 designation are used in a variety of environments. Bases for large wind turbines is one such environment. Bridges are another site for M42 bolts.
Offshore oil rigs are yet another structure in which these bolts are installed. Each of these locations is subjected to different types of force. However, in each instance, the M42 bolts must maintain a precise clamp force between the two component that are to be joined by the bolts.
Fine pitch M42 bolts of high grades provide more margin for error than do coarse pitch bolts of lower grade. After installation, the M42 bolts must be inspected. Go and no-go gauges can be used to check whether the threads of the M42 bolts are still within tolerance.
Optical comparators can help the inspector in measuring the angle of the flanks of the threads of the M42 bolts. An inspection is necessary to ensure that the bolts will not become loose over time. The three most important variables of M42 bolts is pitch, grade, and coating.
Once these three elements of the M42 bolt are correctly selected, all other variables become secondary.
