American National Standard Machine Screws and Machine Screw Nuts
Slotted Set Screws; Pull Dowel Pins 7979 D; Pull Dowel Pin 7979DNF; Threaded Taper Pins; Pipe Plugs & Grease Fittings. Pipe Plugs; Fitting Caps 7605; Grease Fittings; Grease Fittings Assortments; Slotted Machine, Self-Tapping & Thread Forming Screws. Slotted Machine Screws; Cross Recessed Machine Screws; Large Slotted Pan Head Screws 921. Product Catalog » Machine screws » Machine screws » Slotted round head Machine screws, Slotted round head, Aluminum Machine screw diameter is measured on the outside of the threads. Combo Pan Head Zinc Plated Machine Screw (6-Pack) Machine screws are fully threaded fasteners Machine screws are fully threaded fasteners with a uniform diameter the entire length of the shaft. They are primarily used to fasten metal parts together.
This Standard ANSI B18.6.3 covers both slotted and recessed head machine screws. Dimensions of various types of slotted machine screws, machine screw nuts, and header points are given in Tables 1 through 12. The Standard also covers flat trim head, oval trim head and drilled fillister head machine screws and gives cross recess dimensions and gaging dimensions for all types of machine screw heads. Information on metric machine screws B18.6.7M is given beginning on page 1708.
Threads
Except for sizes 0000, 000, and 00, machine screw threads may be either Unified Coarse (UNC) and Fine thread (UNF) Class 2A (see American Standard for Unified Screw Threads starting on page 1865) or UNRC and UNRF Series, at option of manufacturer. Thread dimensions for sizes 0000, 000, and 00 are given in Table 7 on page 1698.
Threads for hexagon machine screw nuts may be either UNC or UNF, Class 2B, and for square machine screw nuts are UNC Class 2B.
Length of Thread
Machine screws of sizes No. 5 and smaller with nominal lengths equal to 3 diameters and shorter have full form threads extending to within 1 pitch (thread) of the bearing surface of the head, or closer, if practicable. Nominal lengths greater than 3 diameters, up to and including 1 1⁄8 inch, have full form threads extending to within two pitches (threads) of the bearing surface of the head, or closer, if practicable. Unless otherwise specified, screws of longer nominal length have a minimum length of full form thread of 1.00 inch. Machine screws of sizes No. 6 and larger with nominal length equal to 3 diameters and shorter have full form threads extending to within 1 pitch (thread) of the bearing surface of the head, or closer, if practicable. Nominal lengths greater than 3 diameters, up to and including 2 inches, have full form threads extending to within 2 pitches (threads) of the bearing surface of the head, or closer, if practicable. Screws of longer nominal length, unless otherwise specified, have a minimum length of full form thread of 1.50 inches.
Table 1. Square and Hexagon Machine Screw Nuts ANSI B18.6.3-1972 (R1991)
All dimensions in inches. Hexagon machine screw nuts have tops flat and chamfered. Diameter of top circle should be the maximum width across flats within a tolerance of minus 15 percent. Bottoms are flat but may be chamfered if so specified. Square machine screw nuts have tops and bottoms flat without chamfer.
Diameter of Body
The diameter of machine screw bodies is not less than Class 2A thread minimum pitch diameter nor greater than the basic major diameter of the thread. Cross-recessed trim head machine screws not threaded to the head have an 0.062 in. minimum length shoulder under the head with diameter limits as specified in the dimensional tables in the standard.
Designation
Machine screws are designated by the following data in the sequence shown: Nominal size (number, fraction, or decimal equivalent); threads per inch; nominal length (fraction or decimal equivalent); product name, including head type and driving provision; header point, if desired; material; and protective finish, if required. For example:
- ¼ - 20 × 1 ¼ Slotted Pan Head Machine Screw, Steel, Zinc Plated
- 6 - 32 × ¾ Type IA Cross Recessed Fillister Head Machine Screw, Brass
Machine screw nuts are designated by the following data in the sequence shown: Nominal size (number, fraction, or decimal equivalent); threads per inch; product name; material; and protective finish, if required. For example:
- 10 - 24 Hexagon Machine Screw Nut, Steel, Zinc Plated
- 0.138 - 32 Square Machine Screw Nut, Brass
Table 2. American National Standard Slotted 100-Degree Flat Countersunk Head Machine Screws ANSI B18.6.3-1972 (R1977)
a When specifying nominal size in decimals, zeros preceding the decimal point and in the fourth decimal place are omitted.
All dimensions are in inches.
Slotted Truss Head Machine Screws
Table 3. American National Standard Slotted Flat Countersunk Head and Close Tolerance 100-Degree Flat Countersunk Head Machine Screws ANSI B18.6.3-1972 (R1991)
a When specifying nominal size in decimals, zeros preceding the decimal point and in the fourth decimal place are omitted.
b These lengths or shorter are undercut.
c May be rounded or flat.
All dimensions are in inches.
Table 4. American National Standard Slotted Undercut Flat Countersunk Head and Plain and Slotted Hex Washer Head Machine Screws ANSI B18.6.3-1972 (R1991)
a When specifying nominal size in decimals, zeros preceding the decimal point and in the fourth decimal place are omitted.
b These lengths or shorter are undercut.
a Unless otherwise specified, hexagon washer head machine screws are not slotted.
All dimensions are in inches.
Table 5. American National Standard Slotted Truss Head and Plain and Slotted Hexagon Head Machine Screws ANSI B18.6.3-1972 (R1991)
a Where specifying nominal size in decimals, zeros preceding decimal points and in the fourth decimal place are omitted.
a Unless otherwise specified, hexagon head machine screws are not slotted.
All dimensions are in inches.
Table 6. American National Standard Slotted Pan Head Machine Screws ANSI B18.6.3-1972 (R1991)
a Where specifying nominal size in decimals, zeros preceding decimal and in the fourth decimal place are omitted.
All dimensions are in inches.
Table 7. Nos. 0000, 000 and 00 Threads ANSI B18.6.3-1972 (R1991) Appendix
a Where specifying nominal size in decimals, zeros preceding decimal and in the fourth decimal place are omitted.
b There is no allowance provided on the external threads.
c The minor diameter limits for internal threads are not specified, they being determined by the amount of thread engagement necessary to satisfy the strength requirements and tapping performance in the intended application.
All dimensions are in inches.
Hex Head Screws
Table 8. American National Standard Slotted Fillister and Slotted Drilled Fillister Head Machine Screws ANSI B18.6.3-1972 (R1991)
All dimensions are in inches.
1 Where specifying nominal size in decimals, zeros preceding decimal points and in the fourth decimal place are omitted.
2 Drilled hole shall be approximately perpendicular to the axis of slot and may be permitted to break through bottom of the slot. Edges of the hole shall be free from burrs.
3 A slight rounding of the edges at periphery of head is permissible provided the diameter of the bearing circle is equal to no less than 90 percent of the specified minimum head diameter.
Table 9. American National Standard Slotted Oval Countersunk Head Machine Screws ANSI B18.6.3-1972 (R1991)
a When specifying nominal size in decimals, zeros preceding decimal points and in the fourth decimal place are omitted.
b These lengths or shorter are undercut.
All dimensions are in inches.
Table 10. American National Standard Header Points for Machine Screws before Threading ANSI B18.6.3-1972 (R1991)
All dimensions in inches. Edges of point may be rounded and end of point need not be flat nor perpendicular to shank. Machine screws normally have plain sheared ends but when specified may have header points, as shown above.
Table 11. American National Standard Slotted Binding Head and Slotted Undercut Oval Countersunk Head Machine Screws ANSI B18.6.3-1972 (R1991)
a Where specifying nominal size in decimals, zeros preceding decimal points and in the fourth decimal place are omitted.
b Unless otherwise specified, slotted binding head machine screws are not undercut.
a These lengths or shorter are undercut.
All dimensions are in inches.
Table 12. Slotted Round Head Machine Screws ANSI B18.6.3-1972 (R1991) Appendix
a When specifying nominal size in decimals, zeros preceding decimal point and in the fourth decimal place are omitted.
All dimensions are in inches.
Not recommended, use Pan Head machine screws.
Machine Screw Cross Recesses
Four cross recesses, Types I, IA, II, and III, may be used in lieu of slots in machine screw heads. Dimensions for recess diameter M, width N, and depth T (not shown above) together with recess penetration gaging depths are given in American National Standard ANSI B18.6.3-1972 (R1991) for machine screws, and in ANSI/ASME B18.6.7M-1985 for metric machine screws.
ANSI Cross Recesses for Machine Screws and Metric Machine Screw
Slotted Hex Head Bolts
Summary
This article presents information about standard machine screws and nuts, including the different types and tables of sizes with key dimensions. Learn more about fasteners from the Machinery's Handbook, 30th Edition, which is published and available from Industrial Press on Amazon.
Other Machining Articles
More from Hardware
Thomas Industry Update
Stay up to date on industry news and trends, product announcements and the latest innovations.
Related Resources
The History of Pies: A Legend in the Baking
Reflection Window + Wall Sets up Indiana Subsidiary: “We Think Indiana Is Going to Be the Factory Floor of the U.S.”
Georgia Manufacturer Chart Industries Acquires Water Technology Firm
Eastern Wholesale Fence to Add $17.5 Million Facility in North Carolina
Feast on These Thanksgiving 'By the Numbers' Fun Facts
Browse by Category
866-573-0445
Mon-Fri 8am-5pm EST
My Cart
Your cart is currently empty.
We are working hard to deliver items in a timely manner. Due to increased safety measures we are taking, orders may be temporarily delayed beyond our standard shipping times.
316 Stainless Steel Phillips Pan Head Machine Screws
316 Stainless Steel Phillips Flat Head Machine Screws
316 Stainless Steel Slotted Pan Head Machine Screws
316 Stainless Steel Slotted Flat Head Machine Screws
316 Stainless Steel Trim Head Hex Cap Machine Screws
316 Stainless Steel Tamper Proof Star Drive Button Head Machine Screws
Machine Screws Slotted Hex Washer Head Type F
Marine Grade Machine Screws
Allen Head Machine Bolts
316 Stainless Steel Machine Screws are ideal in marine/saltwater environments. 316 stainless is prized for its corrosion resistant properties making these the ideal screw of choice for such corrosive environments. These marine grade machine screws are typically in smaller sizes, come in both pan and flat head with a Phillips drive and are found primarily in drawer sliders and machinery. They can be used either with the matching nut or be installed into a pre-tapped hole. To anyone who needs to work with machine screws near the ocean we recommend these to increase the life of the assembly.