M8 screw or bolt dimensions and sizes are heavy-duty fasteners widely utilized in automotive suspension, engine mounts, heavy furniture assembly, and architectural steelwork. This size has a 8.00mm nominal major diameter and is available in M8 x 1.25 for the coarse series and M8 x 1.0 for the fine series, where 1.25 and 1.0 represent the thread pitch in millimeters. This reference chart follows respective DIN and ISO standards for each head style and DIN 13-1 (coarse series), DIN 13-21 (fine series), and ISO 68-1 standards for the thread dimensions table to ensure compatibility across metric fastening applications.
Disclaimer: Actual dimensions and tolerances may vary slightly depending on head style, manufacturer, or material — always verify with the official product datasheet before use.
M8 x 1.25 Screw & Bolt – DIN 13-1/ISO 68-1
Dimension
Size (mm)
Min
Max
Major Diameter
7.76
7.972
Pitch Diameter
7.042
7.16
Minor Diameter
6.272
6.619
Thread Pitch
1.25
Major Diameter
7.76
7.972
Pitch Diameter
7.085
7.16
Minor Diameter
6.315
6.619
Thread Pitch
1.25
M8 x 1.0 Screw & Bolt – DIN 13-21/ISO 68-1
Dimension
Size (mm)
Min
Max
Major Diameter
7.794
7.974
Pitch Diameter
7.212
7.324
Minor Diameter
6.596
6.891
Thread Pitch
1.0
Major Diameter
7.794
7.974
Pitch Diameter
7.253
7.324
Minor Diameter
6.637
6.891
Thread Pitch
1.0
M8 x 0.75 Screw & Bolt – DIN 13-21/ISO 68-1
Dimension
Size (mm)
Min
Max
Major Diameter
7.838
7.978
Pitch Diameter
7.391
7.491
Minor Diameter
6.929
7.166
Thread Pitch
0.75
Major Diameter
7.838
7.978
Pitch Diameter
7.428
7.491
Minor Diameter
6.966
7.166
Thread Pitch
0.75
Major Diameter –
The largest diameter of the external thread, measured crest to crest.
This defines the nominal size (e.g., M12 which is 12 mm of nominal major diameter).
Pitch Diameter –
The diameter of an imaginary cylinder where the thread thickness equals
the space between threads. This is the critical dimension for thread fit
(Tolerance classes 2A/3A for Imperial; 6g/4g6g for Metric).
Minor Diameter –
The smallest diameter of the external thread, measured root to root.
This represents the core strength of the fastener and is the theoretical
maximum diameter of the tap drill.
Thread Pitch –
The distance from a point on one thread to the corresponding point on the next.
What is the tap drill size for M8 x 1.25 and M8 x 1.0 screws or bolts?
For metric fasteners, the recommended tap drill size can be calculated using this formula: Major Diameter – Thread Pitch
Therefore, for an M8 x 1.25 screw or bolt (coarse), the recommended tap drill is 6.75mm (often rounded to 6.8mm in standard sets), while for an M8 x 1.0 (fine), it is 7.00mm.
What clearance hole size is needed for an M8 screw or bolt?
For a Close Fit, a 8.40mm drill bit is utilized. For a Normal Fit, a 9.00mm bit is used, and for a Loose Fit, a 10.00mm bit is recommended to allow the fastener body to pass through the assembly without interference.
What is the difference between a bolt and a screw?
The difference is based on the intent of the fastener’s use; If the primary intent is for the fastener to pass through an unthreaded hole and be assembled with a nut, it is a Bolt. In this application, you usually hold the head and turn the nut to apply tension. But if the primary intent is for the fastener to be installed into a threaded (tapped) hole, it is a Screw. In this application, the connection is tightened by turning the head of the fastener itself.
