a) This Standard covers the dimensional requirements for nine product types of inch series bolts and screws Recognized as American National Standard. Also included are appendices covering gaging procedures, grade markings for bolts and screws, formulas on which dimensional data are based, and a specification to assist in identifying a product as being a screw or a bolt. Where questions arise concerning acceptance of product, the dimensions in the tables shall govern over recalculation by formula. Heavy hex structural bolts, formerly covered in ASME B18.2.1, are now covered in ASME B18.2.6.
b) The inclusion of dimensional data in this Standard is not intended to imply that all of the products described herein are stock production sizes. Consumers should consult with suppliers concerning lists of stock production sizes.
All dimensions in this Standard are in inches and apply to unplanted or uncoated product. When plating or coating is specified, the finished product dimensions shall be as agreed upon between supplier and purchaser. Where nominal sizes are expressed in decimals, zeros preceding the decimal and zeros in the fourth decimal place shall be omitted. Symbols specifying geometric characteristics are in accord with ASME Y14.5.
Where specified, options shall be at the discretion of the manufacturer, unless otherwise agreed upon by the manufacturer and purchaser.
As used in this Standard, “short bolt” or “short screw” means a bolt or screw of a diameter-length combination that is required to be threaded for full length, whereas “long bolt” or “long screw” means a bolt or screw of a diameter-length combination that is not threaded for full length. Body length, LB: the distance measured parallel to the axis of the bolt or screw from the under head bearing surface to the last scratch of thread or, for rolled threads, to the top of the extrusion angle. Where specified, the minimum body length (LB, min.) is a criterion for inspection. grip gaging length, LG: the distance measured parallel to the axis of the bolt or screw from the under head bearing surface to the face of a non-counter bored, non-counter sunk standard GO thread ring gage assembled by hand as far as the thread will permit. The maximum grip gaging length (LG, max.) is a criterion for inspection. point length: the length from the pointed end to the first fully formed thread at major diameter as determined by the distance that the point enters into a cylindrical NOT GO major diameter ring gage (refer to Gage 3.1
in ASME B1.2).
thread length : the length from the extreme point of the bolt or screw to the last complete (full form) thread. For bolts and screws in this Standard, other than lag screws, the nominal thread length (LT) is a reference dimension intended for calculation purposes only. transition thread length, Y: the length that includes the length of incomplete threads, the extrusion angle on rolled threads, and tolerances on grip length. Where specified, transition thread length is a reference dimension intended for calculation purposes only. For definitions of terminology not specified in this Standard, refer to ASME B18.12.
Top of Head. Top of head shall be full for mand chamfered, with the diameter of chamfer circle equal to the Maximum width across flats, on square or hex head products and the “B” dimension shown in Table 11for lobed Head screws with a tolerance of −15%.
Width Across Flats. The width across flats of head shall be the overall distance measured perpendicular to the axis of product between two opposite sides of the head in accordance with the notes in respective dimensional tables.
Head Height. head height shall be the overall distance measured parallel to the axis of product from the top of the head to the bearing surface and shall include the thickness of the washer face where provided.
Position of Head. The run out of the flats or lobes of the head shall be no greater than 6% of the maximum width across flats or lobes. For reference purposes, the evaluation shall be made by indicating on the flats or outer surface of lobes while holding the body one bolt diameter from under the head and rotating the part.
The bolt or screw length shall be the distance measured parallel to the axis of product from the bearing surface of the head to the extreme end of the bolt or screw, including the point if the product is pointed.
The body diameter minimum/maximum limits are defined in each of the respective applicable tables. Unless otherwise specified by the purchaser, the body style supplied shall be full-size body.
a) Only bolts and lag screws are permitted to have die seams on their body that exceed the body diameter. Die seams on the body and all other styles of screws that exceed the body diameter are not permitted.
b) For recommended clearance of hole sizes for bolts and screws, refer to ASME B18.2.8.
Unless otherwise specified, bolts need not be pointed. Products designated as screws, with the exception of lag screws, are required to have a chamfered point. The chamfer angle may vary depending on the manufacturing process. When specified, the chamfer angle should be considered a reference dimension only. The presence of a point is to reduce the possibility of damage to the leading threads and promote assemble ability with a tapped hole or nut. Point features not defined in a given product standard are at the discretion of the manufacturer.
Thread Standard. Threads on all products in this Standard, except lag screws, shall meet the requirements of ASME B1.1 . Lag screw thread dimensions are specified in Table 16.
Thread Class. Unless otherwise specified, size limits for standard external thread Class 2A apply prior to coating. The external thread allowance may be used to accommodate the coating thickness on plated or coated parts, provided that the maximum coating thickness is no more than one-fourth of the allowance. Thus, the thread after plating or coating is subject to acceptance using a basic size Class 3A GO size thread gage and a Class 2A NOT GO size thread gage.
Thread Series. Thread series on all bolts and screws may be coarse (UNC), fine (UNF), or 8 thread series (8 UN), except askew head bolts, which shall be unified coarse (UNC) only, and lag screws, which are specified in Table 16.
Incomplete Thread Diameter. The major diameter of incomplete thread shall not exceed the actual major diameter of the full form thread.
Thread Acceptability. Unless otherwise specified by the purchaser, dimensional acceptability of screw threads shall be determined using thread gaging System 21 in ASME B1.3.
Shanks of bolts and screws shall be straight within the following limits at maximum material condition (MMC).For bolts with nominal lengths up to and including 12 in., the maximum camber shall be 0.006 in. per inch(0.006L) of bolt or screw length. For bolts and screws with nominal lengths over 12 in. up to and including 24 in., the maximum camber shall be 0.008 in. per inch(0.008L) of bolt or screw length. A typical gage and gaging procedure for checking bolt and screw straightness are given in ASME B18.2.9.
For parts that require machining, it may be necessary to provide support with a countersunk center hole in the threaded end. Unless otherwise specified by the purchaser, the drill size and depth shall be in accordance with Non mandatory Appendix C.
Standard materials for various configurations of bolts and screws are identified in paras. 3.9, 4.9, and 5.7. When materials and/or grades, other than those in the applicable notes, are required, the purchaser must clearly specify them in the purchase documents.
Unless otherwise specified, bolts and screws shall be supplied with a plain (as processed) finish, unplanted, or uncoated. Light oil on the surface is permissible to avoid corrosion during transportation, packaging, and further handling.
Surface discontinuities shall be in accordance with the requirements of the applicable fastener material standard. The purchaser may specify additional surface discontinuity requirements for screws and bolts when tighter control of surface discontinuities is required or when discontinuity limits are not specified in the applicable fastener material standard.
Bolts and screws shall be designated by the following data in the sequence shown: product name; nominal size (fractional or decimal equivalent); threads per inch (omit for lag screws); product length (fractional or two-place decimal equivalent); material, including specification where necessary; and protective finish, if required. See the following examples :
a) Square Bolt per ASME B18.2.1, 3⁄8 – 16 _ 11⁄2. Steel per ASTM A 307 Grade A, Zinc plated per ASTM F 1941 Fe/Zn 3A
b) Hex Cap Screw per ASME B18.2.1. 1⁄2 – 13 _ 4. ASTM A 354 Grade BD, plain finish c) Hex Lag Screw per ASME B18.2.1, 0.75 _ 5.00, Stainless Steel per ASTM F 593, Group 1, Condition CW (304)
For a recommended part identification number (PIN) system for B18 fasteners, see ASME B18.24.
Identification Symbols. Identification marking symbols on products included in this Standard shall be raised or indented at the manufacturer’s option unless otherwise specified. Markings shall be legible to the unaided eye with the exception of corrective lenses.
When raised, the height of the marking may not exceed0.015 in. over the specified maximum head height for bolts 5⁄8 in. and smaller. For bolts larger than 5⁄8 in., the marking may not project more than 0.030 in. over the specified maximum head height. When indented, the depth of the marking shall not reduce the load-carrying capacity of the fastener.
Grade Symbols. Each of the products included in this Standard shall be marked in accordance with the Requirements of the applicable specification for its material, mechanical, or performance requirements.
Source Symbols. Each of the products included in this Standard shall be marked in accordance with the requirements of the applicable specification for its material, mechanical, or performance requirements to identify its source, manufacturer, or private label distributor.
Unless otherwise specified, products shall be furnished in accordance with ASME B18.2.
Unless otherwise specified, products shall be furnished in Bolts shall be marked accordance with ASTM A193.
Heavy Hex bolts according to this document shall be marked with:
a) Property class marking in accordance with ASTM A193.
b) Identification mark of the RFL.
It is permissible for the marking to be either embossed or indented on the top surface of the head.