M8 Hex Bolt (Hex Head Bolt), ISO 4014

The M8 hex bolt to ISO 4014 has a hexagon head 12.73 to 13 mm across the flats and 5.3 mm high. Its M8 × 1.25 thread comes in 8 lengths from 40 to 80 mm, each as simplified and threaded STEP.

How these parts are made, and what the levels mean: read the method

• Also searched as: M8 bolt, M8 x 40 to M8 x 80 bolts
• Model id: iso4014-m8
• Standard: ISO 4014:2022 · thread M8 × 1.25, ISO metric coarse, right hand

Lengths

Length (mm)	Part key	Simplified	Threaded
40	iso4014-m8x40	STEP	STEP
45	iso4014-m8x45	STEP	STEP
50	iso4014-m8x50	STEP	STEP
55	iso4014-m8x55	STEP	STEP
60	iso4014-m8x60	STEP	STEP
65	iso4014-m8x65	STEP	STEP
70	iso4014-m8x70	STEP	STEP
80	iso4014-m8x80	STEP	STEP

Dimensions

Symbol	Name	min	nom	max	Modeled	Rule	Level
P	Thread pitch		1.25		1.25	nominal	L2
a	Thread run-out under the head (ISO 4017)	1.25		3.75	2.5	midpoint of min–max	L2
b	Thread length (ISO 4014)		22 ref		22	reference value	L2
c	Washer face height	0.15		0.6	0.375	midpoint of min–max	L2
da	Transition diameter			9.2	9.2	single limit (max), modeled at the limit	L2
ds	Shank diameter (ISO 4014)	7.78		8	7.89	midpoint of min–max	L2
dw	Bearing face diameter	11.63			11.63	single limit (min), modeled at the limit	L2
e	Width across corners	14.38			14.38	single limit (min), modeled at the limit	L2
k	Head height	5.15	5.3	5.45	5.3	nominal	L2
kw	Wrenching height	3.61			3.61	single limit (min), modeled at the limit	L2
beta	Head top chamfer angle	15		30	22.5	midpoint of min–max	L2
lf	Fillet transition length (ISO 4014)			2	2	single limit (max), modeled at the limit	L2
r	Underhead fillet radius	0.4			0.4	single limit (min), modeled at the limit	L2
s	Width across flats	12.73		13	12.865	midpoint of min–max	L2
P	Coarse thread pitch		1.25		1.25	nominal	L1
tap_drill	Tap drill diameter		6.75		6.75	nominal	L1
d1	Basic minor diameter		6.646835		6.646835	nominal	L1
ch_angle	Chamfered end angle			50	50	single limit (max), modeled at the limit	L2
dh_fine	Clearance hole, fine series		8.4		8.4	nominal	L1
dh_medium	Clearance hole, medium series		9		9	nominal	L1
dh_coarse	Clearance hole, coarse series		10		10	nominal	L1

Thread and holes

• Tap drill: 6.75 mm (method: d − P), L1, sources amesweb-tap-drill, rule-tap-drill.
• Clearance hole (ISO 273): close 8.4, normal 9, loose 10 mm (L1: fine, medium and coarse series (albany-clearance, wikipedia-de-clearance)).

Drawing

As a PDF: CC-ISO4014-SZ-M8.pdf.

Goes with the M8 hex bolt

• Spanner: 13 mm, the hexagon's maximum width across flats (s) in the table above.
• ISO 4032 hex nut, the same size as this M8 hex bolt: M8 Hex Nut (Hexagon Nut), ISO 4032 / DIN 934
• ISO 7089 flat washer, the same size as this M8 hex bolt: M8 Flat Washer (Plain Washer), ISO 7089

The M8 hex bolt beside the M6

The M8 is the largest of the 7 ISO 4014 hex bolts published here, from M2 to M8.

• Thread pitch (P): 1.25 mm on the M8 hex bolt, against 1 mm on the M6.
• Thread run-out under the head (ISO 4017) (a): 1.25 to 3.75 mm on the M8 hex bolt, against 1 to 3 mm on the M6.
• Thread length (ISO 4014) (b): 22 mm (reference) on the M8 hex bolt, against 18 mm (reference) on the M6.
• Washer face height (c): 0.15 to 0.6 mm on the M8 hex bolt, against 0.15 to 0.5 mm on the M6.
• Transition diameter (da): up to 9.2 mm on the M8 hex bolt, against up to 6.8 mm on the M6.
• Shank diameter (ISO 4014) (ds): 7.78 to 8 mm on the M8 hex bolt, against 5.82 to 6 mm on the M6.
• Bearing face diameter (dw): at least 11.63 mm on the M8 hex bolt, against at least 8.88 mm on the M6.
• Width across corners (e): at least 14.38 mm on the M8 hex bolt, against at least 11.05 mm on the M6.

Other sizes

• One size smaller: M6 Hex Bolt (Hex Head Bolt), ISO 4014, 9.78 to 10 mm across flats.

Documents

• CC-ISO4014-DS-M8.pdf: M8 datasheet: values with levels, lengths, sources
• CC-ISO4014-SZ-M8.pdf: M8 drawing: this size's values on the views
• parts.json: the part record of every length (the platform contract)

Sources

albany-clearance, amesweb-tap-drill, fasten-it-iso4014, fasten-it-iso4017, fasteners-eu-iso4017, fuller-iso4014, globalfastener-iso4017, globalfastener-iso4017-2022, iso4014-2022-sample, iso4014-2022-sample-lengths, iso4017-2022-sample, iso4017-2022-sample-figure, iso4753-2011-sample, rule-basic-minor, rule-iso4014-lg, rule-tap-drill, wikipedia-de-clearance, wikipedia-iso261. Full citations: the method page and this size's datasheet.

Found an error? Use the feedback section on this page.