Fasteners. GMC Truck GMC C-Series Medium Duty Truck B7 1998

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck B7 🢒 General Information 🢒 General Information 🢒 Fasteners

Table 1:	Metric Prevailing Torque Fastener Minimum Torque Development
Table 2:	English Prevailing Torque Fastener Minimum Torque Development

Metric Fasteners

This vehicle provides fastener dimensions using the metric system. Most metric fasteners are approximate in diameter to equivalent English fasteners. Make replacements using fasteners of the same nominal diameter, thread pitch, and strength.

A number marking identifies the OE metric fasteners except cross-recess head screws. The number also indicates the strength of the fastener material. A Posidrive® or Type 1A cross-recess identifies a metric cross-recess screw. For best results, use a Type 1A cross-recess screwdriver, or equivalent, in Posidrive® recess head screws.

GM Engineering Standards and North American Industries have adopted a portion of the ISO-defined standard metric fastener sizes. The purpose was to reduce the number of fastener sizes used while retaining the best thread qualities in each thread size. For example, the metric M6.0 X 1 screw, with nearly the same diameter and 25.4 threads per inch replaced the English 1/4-20 and 1/4-28 screws. The thread pitch is midway between the English coarse and fine thread pitches.

Fastener Strength Identification


(1)	English Bolt, Grade 2 (Strength Class)
(2)	English Bolt, Grade 5 (Strength Class)
(3)	English Bolt, Grade 7 (Strength Class)
(4)	English Bolt, Grade 8 (Strength Class)
(5)	Metric Nut, Strength Class 9
(6)	Metric Bolts, Strength Class Increases as Numbers Increase

The most commonly used metric fastener strength property classes are 9.8 and 10.9. The class identification is embossed on the head of each bolt. The English, inch strength classes range from grade 2 to grade 8. Radial lines are embossed on the head of each bolt in order to identify the strength class. The number of lines on the head of the bolt is 2 lines less than the actual grade. For example, a grade 8 bolt will have 6 radial lines on the bolt head. Some metric nuts are marked with a single digit strength identification number on the nut face.

The correct fasteners are available through GM SPO. Many metric fasteners available in the aftermarket parts channels are designed to metric standards of countries other than the United States, and may exhibit the following:

•	Lower strength

•	No numbered head marking system

•	Wrong thread pitch

The metric fasteners on GM products are designed to new, international standards. The following are the common sizes and pitches, except for special applications:

•

M6.0 X 1

•

M8 X 1.25

•

M10 X 1.5

•	M12 X 1.75

•	M14 X 2.00

•	M16 X 2.00

Prevailing Torque Fasteners

Prevailing torque fasteners create a thread interface between the fastener and the fastener counterpart in order to prevent the fastener from loosening.

All Metal Prevailing Torque Fasteners

These fasteners accomplish the thread interface by a designed distortion or deformation in the fastener.

Nylon Interface Prevailing Torque Fasteners

These fasteners accomplish the thread interface by the presence of a nylon material on the fastener threads.

Adhesive Coated Fasteners

These fasteners accomplish the thread interface by the presence of a thread-locking compound on the fastener threads. Refer to the appropriate repair procedure in order to determine if the fastener may be reused and the applicable thread-locking compound to apply to the fastener.


(1)	Prevailing Torque Nut, Center Lock Type
(2)	Prevailing Torque Nut, Top Lock Type
(3)	Prevailing Torque Nut, Nylon Patch Type
(4)	Prevailing Torque Nut, Nylon Washer Insert Type
(5)	Prevailing Torque Nut, Nylon Insert Type
(6)	Prevailing Torque Bolt, Dry Adhesive Coating Type
(7)	Prevailing Torque Bolt, Thread Profile Deformed Type
(8)	Prevailing Torque Bolt, Nylon Strip Type
(9)	Prevailing Torque Bolt, Out-of-Round Thread Area Type

A prevailing torque fastener may be reused ONLY if:

•	The fastener and the fastener counterpart are clean and not damaged

•	There is no rust on the fastener

•	The fastener develops the specified minimum torque against its counterpart prior to the fastener seating

Metric Prevailing Torque Fastener Minimum Torque Development

Application	Specification
Application	Metric	English
All Metal Prevailing Torque Fasteners
6 mm	0.4 N·m	4 lb in
8 mm	0.8 N·m	7 lb in
10 mm	1.4 N·m	12 lb in
12 mm	2.1 N·m	19 lb in
14 mm	3 N·m	27 lb in
16 mm	4.2 N·m	37 lb in
20 mm	7 N·m	62 lb in
24 mm	10.5 N·m	93 lb in
Nylon Interface Prevailing Torque Fasteners
6 mm	0.3 N·m	3 lb in
8 mm	0.6 N·m	5 lb in
10 mm	1.1 N·m	10 lb in
12 mm	1.5 N·m	13 lb in
14 mm	2.3 N·m	20 lb in
16 mm	3.4 N·m	30 lb in
20 mm	5.5 N·m	49 lb in
24 mm	8.5 N·m	75 lb in

English Prevailing Torque Fastener Minimum Torque Development

Application	Specification
Application	Metric	English
All Metal Prevailing Torque Fasteners
1/4 in	0.5 N·m	4.5 lb in
5/16 in	0.8 N·m	7.5 lb in
3/8 in	1.3 N·m	11.5 lb in
7/16 in	1.8 N·m	16 lb in
1/2 in	2.3 N·m	20 lb in
9/16 in	3.2 N·m	28 lb in
5/8 in	4 N·m	36 lb in
3/4 in	7 N·m	54 lb in
Nylon Interface Prevailing Torque Fasteners
1/4 in	0.3 N·m	3 lb in
5/16 in	0.6 N·m	5 lb in
3/8 in	1 N·m	9 lb in
7/16 in	1.3 N·m	12 lb in
1/2 in	1.8 N·m	16 lb in
9/16 in	2.5 N·m	22 lb in
5/8 in	3.4 N·m	30 lb in
3/4 in	5 N·m	45 lb in

Fasteners Metric Fasteners

Notice: Always use the correct fastener in the proper location. When you replace a fastener, use ONLY the exact part number for that application. General Motors will call out those fasteners that require a replacement after removal. General Motors will also call out the fasteners that require thread lockers or thread sealant. UNLESS OTHERWISE SPECIFIED, do not use supplemental coatings (paints, greases, or other corrosion inhibitors) on threaded fasteners or fastener joint interfaces. Generally, such coatings adversely affect the fastener torque and the joint clamping force, and may damage the fastener. When you install fasteners, use the correct tightening sequence and specifications. Following these instructions can help you avoid damage to parts and systems.

Current model General Motors vehicles are dimensioned primarily in the metric system. Many fasteners are metric and are very close in dimension to fasteners in the inch system. Replace the fasteners using the following identical specifications:

•	The nominal diameter

•	The thread pitch

•	The strength

Most stock metric fasteners have numbers indicating the strength of the material in the fastener. "Beauty" bolts, such as exposed bumper bolts have no strength indicator. Identify metric cross-recess screws by a Posidriv® or Type 1A marking. Use a Type 1A cross-recess screwdriver in order to fasten or unfasten metric cross-recess screws. If a Type 1A cross-recess screwdriver is not available, use a Phillips head screwdriver.

General Motors Engineering Standards and other North American industries use a portion of the standard metric fastener sizes defined by the International Standards Organization (ISO). Now the total number of fastener sizes in use is lower, and the overall strength quality of each thread size is higher.

For example, the metric M6.0 x 1 screw replaces the English ¼-20 and ¼-28 screws, which have nearly the same diameter. The thread pitch, 25.4 threads per inch, is between coarse and fine thread pitches in English. Metric and English thread notations differ slightly. The thread major diameter of a 1/4-20 bolt is 1/4-inch, and the bolt has 20 threads per inch. The thread major diameter of a 6.0 x 1 bolt is 6.0 mm, and the distance between threads is 1 mm.

Fasteners Prevailing Torque Fasteners

Table 1:	Metric Fasteners (Prevailing Torque)
Table 2:	English Fasteners (Prevailing Torque)

Engineers design prevailing torque nuts in order to develop an interference between the nut and bolt threads. Usually the interference is caused by distorting the top of a metal nut (1, 2) or by a nylon patch on the threads in the middle of the hex flat (3). A nylon insert between the nut and bolt threads also may cause the interference (4, 5).

Engineers design prevailing torque bolts in order to develop an interference between the bolt and nut threads, or the threads of a tapped hole. The interference is caused by distorting some of the threads using one of the following methods:

•	A nylon patch (8)

•	Adhesive (6)

•	A deformed thread profile (7)

•	An out of round thread area (9)

Recommendations for Reuse

Perform the following steps in order to reuse clean, non-rusted, prevailing torque nuts:

Clean dirt and other foreign material off of the nuts and bolts.
Inspect the nuts or bolts for the following conditions. If any of the following conditions exist, use a new prevailing torque fastener:

•

Cracks

•

Rust

•

Damage

•	Elongation

•	Signs of abuse

•	Signs of overtightening

Assemble the parts.
Hand start the nuts or bolts.
Ensure that the fastener develops proper torque before the fastener seats. Refer to the Torque Table. If the proper torque does not develop, use a new prevailing torque fastener.
Tighten the fastener to the torque specified in the appropriate fastener tightening specification.

Metric Fasteners (Prevailing Torque)

Fastener Type	Specification
Fastener Type	Metric	English
Nuts/Metal Bolts
6	0.4 N·m	4 lb in
6.3	0.4 N·m	4 lb in
8	0.8 N·m	7 lb in
10	1.4 N·m	12 lb in
12	2.2 N·m	19 lb in
14	3.0 N·m	27 lb in
16	4.2 N·m	37 lb in
Adhesive or Nylon Coated Bolts
6	0.4 N·m	4 lb in
6.3	0.4 N·m	4 lb in
8	0.6 N·m	5 lb in
10	1.2 N·m	11 lb in
12	1.6 N·m	14 lb in
14	2.4 N·m	21 lb in
16	3.4 N·m	30 lb in

English Fasteners (Prevailing Torque)

Fastener Type/Torque Units	Specification
Fastener Type/Torque Units	Metric	English
Nuts/Metal Bolts
0.250	0.4 N·m	4 lb in
0.312	0.6 N·m	5 lb in
0.375	1.4 N·m	12 lb in
0.437	1.8 N·m	16 lb in
0.500	2.4 N·m	21 lb in
0.562	3.2 N·m	28 lb in
0.625	4.2 N·m	37 lb in
Adhesive or Nylon Coated Bolts
0.250	0.4 N·m	4 lb in
0.312	0.6 N·m	5 lb in
0.375	1.0 N·m	9 lb in
0.437	1.4 N·m	12 lb in
0.500	1.8 N·m	16 lb in
0.562	2.6 N·m	23 lb in
0.625	3.4 N·m	30 lb in

Fasteners Strength Identification

Fastener Strength Identification


(1)	English Bolt, Grade 2 (Strength Class)
(2)	English Bolt, Grade 5 (Strength Class)
(3)	English Bolt, Grade 7 (Strength Class)
(4)	English Bolt, Grade 8 (Strength Class)
(5)	Metric Nut, Strength Class 9
(6)	Metric Bolts, Strength Class Increases as Numbers Increase

Notice: The designation of the standard fasteners used on this vehicle are of coarse screw thread up to M8 and fine screw thread beyond M10. The designation to pitch relations are somewhat different between coarse screw thread and fine screw thread. Therefore, when replacing fasteners, the pitch should be confirmed carefully even if the replacement fastener is the same metric fastener.

The most common metric fastener strength property classes are 9.8 and 10.9. The class identification number is embossed on the head of each bolt (6). Some metric nuts are marked with single digit strength identification numbers on the nut face.

English strength classes range from 2 (low strength) to 8 (high strength). A grade-2 bolt has no lines embossed on the bolt head (1). One radial line is embossed on the bolt head for each strength grade above 2. That is, a bolt with one embossed line indicates grade-3. Two embossed lines indicate grade-4. Six embossed lines signify grade-8, the highest-grade bolt (4).

Correct replacement bolts and nuts are available through General Motors Service Parts Operations (GMSPO). Many metric fasteners available in the after-market parts channels are designed to foreign metric standards, and may have a different thread pitch. Isuzu products use metric fasteners designed to new, international standards. Some non-domestic bolt and nut suppliers may not yet use the international standards.

Fasteners (Strength Identification)

Metric Coarse Screw Threads				Metric Fine Screw Threads
Thread	Pitch	Thread	Pitch	Thread	Pitch	Thread	Pitch
M39	4	M8	1.25	M39x3	3	M20x1.5	1.5
M36	4	M7	1	M36x3	3	M18.1.5	1.5
M33	3.5	M6	1	M33x2	2	M16x1.5	1.5
M30	3.5	M5x0.8	0.8	M30x2	2	M14x1.5	1.5
M27	3	M4x0.7	0.75	M27x2	2	M12x1.25	1.25
M24	3	M4x0.7	0.7	M24x2	2	M10x1.25	1.25
M22	2.5	M3.5	0.6	M22x1.5	1.5	M8x1	1
M20	2.5	M3x0.5	0.5	--	--	--	--
M18	2.5	M2.5	0.45	--	--	--	--
M16	2	M2.2	0.45	--	--	--	--
M14	2	M2	0.4	--	--	--	--
M12	1.75	M1.6	0.35	--	--	--	--
M10	1.5	--	--	--	--	--	--