So Fix it

Tightening bolts to the proper torque is extremely important. Bolts that are not tightened enough can fail to provide the necessary support and stability, and bolts that are tightened too much can actually snap unexpectedly, particularly when you apply additional pressure. There are several factors to consider when calculating bolt torque specs, including the grade, size and purpose of the bolt, and the fastener that is catching it. If a bolt should be tightened to 2,000 inch-pounds of torque, but the fastener can only withstand 1,000 inch-pounds, there is a good chance the fastener will bend or break as the bolt is tightened.

Types of Stainless Steel

The two main types of steel used in stainless steel bolts are 18-8 stainless steel and 316 stainless steel. Stainless steel given an 18-8 designation consists of approximately 18 percent chromium and 8 percent nickel. The remainder of the steel comprises several other elements and compounds, including manganese, phosphorus, sulfur, silicon and chromium. Carbon is held to a maximum of 0.08 percent in both basic types of stainless steel. The term 18-8 applies to several similar grades of steel, including types 302, 303, 304, 305 and 384. These types of stainless steel represent the "basic alloy," and there is little difference between them in terms of strength or resistance to corrosion. Type 316 stainless steel is similar to 18-8 stainless steel except that it is more resistant to corrosion because there are higher levels of molybdenum in it. Type 316 stainless steel is often used in marine situations because it is particularly more resistant to corrosion caused by salt water.

Size, Thread Count and Other Factors

In addition to the grade of stainless steel the bolt is composed of, several other factors, such as the length of the bolt, the bolts thread count, the job that the bolt is being used for, the fastener the bolt is being applied to, any plating the bolt has been coated in and whether or not the bolt is clean, dry or lubricated can affect the the amount of torque that should be applied to a bolt. For instance, a 5/16 bolt with 24 threads per inch requires more torque than a 1/4 inch bolt with 28 threads per inch. The Rask Cycle website recommends lubricating motorcycle bolts with motor oil to reduce the torque by 15 percent to 25; to reduce torque by 50 percent, use a Teflon dry film or a Cetyl alcohol dry wax.

Bolt Torque Specs

Taking the above factors into consideration, the following specs provide a good ball-park range for the perred fastening torque of several bolts. The torque is given in inch-pounds and is intended for standard bolts (without plating) that are dry at the time of tightening.

You should tighten bolts that are 1/4 of an inch long and made of 18-8 stainless should to 75.2 inch-pounds if they have 20 threads per inch and to 94 inch-pounds if they have 28 threads per inch. Tighten bolts of the same size and thread count that are made of 316 stainless steel to 78.8 inch-pounds and 99.0 inch-pounds, respectively.

Tighten bolts that are 3/4 of an inch long and made of 18-8 stainless steel to 1,530 inch-pounds if they have 10 threads per inch and to 1,490 inch-pounds if they have 16 threads per inch. With bolts of the same size and thread count that are made of 316 stainless steel, tighten to 1,582 inch-pounds and 1,588 inch-pounds, respectively.

Tighten one inch long bolts that are made of 18-8 stainless steel to 3,440 inch-pounds if they have 8 threads per inch and to 3,110 inch-pounds if they have 14 threads per inch. Bolts of the same size and thread count that are made of 316 stainless steel should be tightened to 3,595 inch-pounds and 3,250 inch-pounds, respectively.

When cutting stainless steel tubing, you must ensure that the cut end of the stainless tubing is straight. If the cut is crooked, the end that you cut will not fit squarely into a stainless steel fitting or butt up tight to another piece of pipe for a weld joint. The tools required to mark a straight cut on the stainless steel tubing are relatively simple, readily available and inexpensive. Selecting the proper tool to cut the squarely marked tubing is vital to ensuring that the cut is straight.

Instructions

1

Stretch the tape measure along the stainless steel tubing and mark the length you need to cut with a permanent marker.

2

Place the marked length of tubing into a table-mounted vise. Slide the length mark 12 inches past the end of the vise and turn the handle of the vise clockwise to secure the tubing.

3

Fold an 8 1/2-inch by 11-inch piece of paper into a two-inch-wide strip that is 11 inches long.

4

Align one side of the folded paper with the length mark you placed on the stainless steel tubing. Wrap the paper around the tubing and pinch the ends of the paper together. When the edges of the folded paper are even, the paper line is straight.

5

Run the permanent marker around the edge of the folded paper, marking a straight line around the stainless steel tubing. Remove the paper from the tubing.

6

Attach a .032 abrasive cut-off wheel to a four-inch grinder.

7

Put on your safety glasses, face shield and leather work gloves.

8

Cut 1/4 of the circumference of the stainless steel tubing, pressing the cutting wheel slowly along the cut mark.

9

Loosen the table vise, spin the tubing 1/4 of a turn and tighten the vise. Continue cutting the tubing.

10

Replace the abrasive cut-off wheel when it wears to the cutting line, or roughly 60 percent of the cut-off wheels original diameter.

11

Complete the cutting process and set the grinder aside. Run a fine-tooth half-round file around the inside and outside of the cut to remove sharp burrs left by the cutting wheel.

Stainless steel bolts are popular fasteners because of their strength and resistance to corrosion. While in many households bolts are tightened until they feel tight enough, industries and car mechanics require specific torque values for bolts to ensure that they are tightened enough. Depending on the bolt size, construction, fabric, and lubrication, torque specifications vary from bolt to bolt and situation to situation, and should be followed precisely.

Sizes and Threads

Bolts are identified by their sizes and threads. Screws can be as small as the number one screw, which is 1/16 of an inch or as large as the number 24, which is 3/8 of an inch for the most common screw sizes. Their threads are listed by distance between the threads and number per screw, and are listed like this: 1/4 x 20, meaning that the screw has a diameter of 1/4 of an inch and has 20 threads per inch.

Types

Stainless steel bolts come in numerous types, the most common of which are called 18-8 and 316. The 18-8 stainless steel bolt is composed of about 18 percent chromium and 8 percent nickel. These bolts are extremely corrosion resistant. The 316 stainless steel bolt, designed for industrial environments, has a higher nickel content and is austenitic (tempered for strength at low temperatures) and non-magnetic. These stainless steel bolts hold up under extreme stress and are used in heavy industry and as a part of surgical implants for humans and animals.

Torque Specifications

The 2-56 bolts are two inches in diameter with 56 threads per inch, torque to 2.5 inch-pounds for 18-8 stainless steel and to 2.6 inch-pounds for 316 stainless steel. Bolts that are 4 inches in diameter and have 40 threads per inch require 5.2 inch-pounds of torque if they are 18-8 stainless steel and 5.5 inch-pounds of torque if they are 316 stainless steel. For 18-8 stainless steel bolts with a size of 6-32, torque to 9.6 inch-pounds; for 316 stainless steel bolts of the same size, torque to 10.0 inch-pounds. The 1-14 bolts made of 18-8 stainless steel torque to 3110 inch-pounds, and those made of 316 stainless steel torque to 3250 inch-pounds.

Variations

These and other torque specifications for bolts are a starting point, but variation exists depending on the type and amount of lubrication used. If youd like to calculate your own torque, you can apply the following formula: Torque = 1.33 times the coefficient of friction times the diameter times the necessary preload, or T = K x U x D x P. Use 0.2 as the coefficient of friction for dry, or un-lubed fasteners and 0.09 for lubed ones. These are not precise values, but are acceptable averages.

To determine preload, take the established ultimate strength of your fastener (this information will be available at your hardware store), and multiply it by 2/3 to determine yield strength. Multiply the bolts thread area by the full yield strength and 2/3 to determine its preload. Once youve filled in these values, you can determine your bolts required torque.