M2.5 Hex Bolt (Hex Head Bolt), ISO 4014

Across the flats of its hexagon head, an M2.5 hex bolt (ISO 4014) measures 4.82 to 5 mm; the head is 1.7 mm high. Here in 3 lengths from 16 to 25 mm, each as simplified and threaded STEP.

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

• Also searched as: M2.5 bolt, M2.5 x 16 to M2.5 x 25 bolts
• Model id: iso4014-m2-5
• Standard: ISO 4014:2022 · thread M2.5 × 0.45, ISO metric coarse, right hand

Lengths

Length (mm)	Part key	Simplified	Threaded
16	iso4014-m2-5x16	STEP	STEP
20	iso4014-m2-5x20	STEP	STEP
25	iso4014-m2-5x25	STEP	STEP

Dimensions

Symbol	Name	min	nom	max	Modeled	Rule	Level
P	Thread pitch		0.45		0.45	nominal	L2
a	Thread run-out under the head (ISO 4017)	0.45		1.35	0.9	midpoint of min–max	L2
b	Thread length (ISO 4014)		11 ref		11	reference value	L2
c	Washer face height	0.1		0.25	0.175	midpoint of min–max	L2
da	Transition diameter			3.1	3.1	single limit (max), modeled at the limit	L2
ds	Shank diameter (ISO 4014)	2.36		2.5	2.43	midpoint of min–max	L2
dw	Bearing face diameter	4.34			4.34	single limit (min), modeled at the limit	L2
e	Width across corners	5.45			5.45	single limit (min), modeled at the limit	L2
k	Head height	1.575	1.7	1.825	1.7	nominal	L2
kw	Wrenching height	1.1			1.1	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)			1	1	single limit (max), modeled at the limit	L2
r	Underhead fillet radius	0.1			0.1	single limit (min), modeled at the limit	L2
s	Width across flats	4.82		5	4.91	midpoint of min–max	L2
P	Coarse thread pitch		0.45		0.45	nominal	L1
tap_drill	Tap drill diameter		2.05		2.05	nominal	L1
d1	Basic minor diameter		2.0128606		2.0128606	nominal	L1
ch_angle	Chamfered end angle			50	50	single limit (max), modeled at the limit	L2
dh_fine	Clearance hole, fine series		2.7		2.7	nominal	L1
dh_medium	Clearance hole, medium series		2.9		2.9	nominal	L1
dh_coarse	Clearance hole, coarse series		3.1		3.1	nominal	L1

Thread and holes

• Tap drill: 2.05 mm (method: d − P), L1, sources amesweb-tap-drill, rule-tap-drill.
• Clearance hole (ISO 273): close 2.7, normal 2.9, loose 3.1 mm (L1: fine, medium and coarse series (albany-clearance, wikipedia-de-clearance)).

Drawing

As a PDF: CC-ISO4014-SZ-M2.5.pdf.

Goes with the M2.5 hex bolt

• Spanner: 5 mm, the hexagon's maximum width across flats (s) in the table above.
• ISO 4032 hex nut, the same size as this M2.5 hex bolt: M2.5 Hex Nut (Hexagon Nut), ISO 4032 / DIN 934
• ISO 7089 flat washer, the same size as this M2.5 hex bolt: M2.5 Flat Washer (Plain Washer), ISO 7089

The M2.5 hex bolt beside the M2 and the M3

The M2.5 is number 2, counting from the smallest, of the 7 ISO 4014 hex bolts published here, from M2 to M8.

• Thread pitch (P): 0.45 mm on the M2.5 hex bolt, against 0.4 mm on the M2 and 0.5 mm on the M3.
• Thread run-out under the head (ISO 4017) (a): 0.45 to 1.35 mm on the M2.5 hex bolt, against 0.4 to 1.2 mm on the M2 and 0.5 to 1.5 mm on the M3.
• Thread length (ISO 4014) (b): 11 mm (reference) on the M2.5 hex bolt, against 10 mm (reference) on the M2 and 12 mm (reference) on the M3.
• Washer face height (c): 0.1 to 0.25 mm on the M2.5 hex bolt, against 0.1 to 0.25 mm on the M2 and 0.15 to 0.4 mm on the M3.
• Transition diameter (da): up to 3.1 mm on the M2.5 hex bolt, against up to 2.6 mm on the M2 and up to 3.6 mm on the M3.
• Shank diameter (ISO 4014) (ds): 2.36 to 2.5 mm on the M2.5 hex bolt, against 1.86 to 2 mm on the M2 and 2.86 to 3 mm on the M3.
• Bearing face diameter (dw): at least 4.34 mm on the M2.5 hex bolt, against at least 3.34 mm on the M2 and at least 4.84 mm on the M3.
• Width across corners (e): at least 5.45 mm on the M2.5 hex bolt, against at least 4.32 mm on the M2 and at least 6.01 mm on the M3.

Other sizes

• One size smaller: M2 Hex Bolt (Hex Head Bolt), ISO 4014, 3.82 to 4 mm across flats.
• One size larger: M3 Hex Bolt (Hex Head Bolt), ISO 4014, 5.32 to 5.5 mm across flats.

Documents

• CC-ISO4014-DS-M2.5.pdf: M2.5 datasheet: values with levels, lengths, sources
• CC-ISO4014-SZ-M2.5.pdf: M2.5 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.

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