The “Nuts and Bolts” of DRAWING BOLTS AND NUTS

Bolts and nuts aren’t normally drawn on detail drawings unless they are of a special size or have been modified.

On some assembly drawings it may be necessary to show a nut and bolt.

Conventional drawing practice is to show the nuts and bolt heads in the across-corners position in all views.

CONTENTS OF SLIDE SHOW:

Slide # Description

3-4 Just the Facts

5-6 Formulas & Calculations

7 How to Draw Bolts & Nuts

8-12 Hex Head

12-13 Layout of Bolt and Nut

American National Standard bolts and nuts, metric and inch series, are produced in the hexagon form, and the square form is only produced in the inch series.

Although square heads and nuts are chamfered at 30°, and hexagon heads and nuts are chamfered at 15-30°, BOTH are drawn at 30° for simplicity.

JUST THE FACTS:

Both Inch and Metric Bolts are grouped according to their use.

Regular Inch Bolts – general service – square bolts only come in the regular type – hexagon bolts, screws and nuts and square nuts are standard in both types

Heavy Inch Bolts – heavier service or easier wrenching

Regular & Heavy Metric Bolts – general service

High-Strength Metric Bolts & Nuts – for structural bolting

Square bolts and nuts, hexagon bolts and hexagon flat nuts are unfinished. Unfinished bolts and nuts are not machined on any surface except for the threads.

Hexagon cap screws, heavy hexagon screws and all hexagon nuts, except hexagon flat nuts, are considered finished to some degree and are characterized by a “washer face” machined or otherwise formed on the bearing surface.

The washer face is 1/64” thick (drawn 1/32”), and its diameter is equal to 1 ½ times the body diameter D for the inch series.

In Metric, the “washer face is approximately 0.5mm thick (drawn 1mm) and its diameter is equal to 1 ½ times the body diameter D.Lengths of bolts haven’t been standardized because of the endless variety required by industry.

Short bolts are typically available in standard length increments of ¼” (6mm), while long bolts come increments of ½ to 1” (12 to 25mm).

Formulas for exact or “close” approximations of bolts & nuts sizes based on diameter D of the bolt body for drawing purposes:

REGULAR HEXAGON & SQUARE BOLTS & NUTS:

W = 1 ½ D H = 2/3 D T = 7/8 D

W = width across flats, H = head height and T = nut height

HEAVY HEXAGON BOLTS & NUTS & SQUARE NUTS:

W = 1 ½ D + 1/8” (or + 3 mm)

H = 2/3 D T = D

The washer face is ALWAYS included in the head or nut height for finished hexagon screw heads and nuts.

Thread Length Calculations:

Bolts or Screws up to 6” (150mm) in length

Thread length = 2D + ¼” (or +6mm)

Bolts or Screws over 6” in length

Thread length = 2D + ½” (or +12mm)

These formulas can be used to “approximate” bolt sizes for drawing purposes. However, there are charts and tables available in some instances for more precise dimensioning in more detailed drawings.

How to Draw Hex Head Bolts & Nuts

The following slides will layout the “how to” as to drawing bolts and nuts.

In the examples, we will use a 7/8” (.875”) – 9UNC Hex Head Bolt

Once you’ve drawn the bolt diameter and established the centerline, by using : 2/3 * Dia. of the Bolt, let’s set up the hex head for the bolt.

.666 * .875 = .58275 ≈ .603 ≈ 5/8”The thickness or height of the bolt head can be determined.

Extend the bolt centerline so as to layout the head of the bolt in a top view.

1 ½ * Dia of the Bolt =

1 ½ * .875 = 1.3125

1.3125 = the dia. of the circle to be used to circumscribe the 6-sided polygon around. Use construction lines to determine

the corners of the bolt head in the front view.

Centerpoint

Remember: Generally bolt heads and nuts should be drawn “across corners” in all views.

Horizontal line thru endpoints of original arc.

When you get rid of your construction lines, your finished Hex Head will look like the one at left.

Okay, now you’ve got the head of the bolt drawn let’s move on to the threads and the nut.

Using the Hex Head of the bolt, draw construction lines down the length of the bolt. These will be used for drawing the nut.

From the bottom of the bolt and using and arbitrary dimension of ¼”, offset the line up from the bottom of the bolt. From that line, and using the formula:

7/8 * D

= .875 & .875

= .7656 ≈ ¾

This gives us the approximate thickness of the nut as being ¾”

Using the same steps as when drawing the hex head, you can now draw in the nut at the lower end of the bolt.

ThanksReferences:

Helsel, Jay D. and Cecil Jensen. Engineering Drawing & Design 5th/6th Ed. 1996. Glencoe McGraw-Hill. Westerville, Ohio.