What is the weight of an M20 Allen bolt?

An M20 x 50 socket head cap screw weighs about 191 g and an M20 x 100 about 313 g. Each extra 10 mm of thread adds roughly 21 g.

How many Allen bolts are there in 1 kg?

It depends on size and length: about 74 pieces of M8 x 20, 17 of M12 x 50, 9 of M16 x 50 and 2 of M24 x 100.

Does a 12.9 socket head cap screw weigh more than an 8.8?

No. Property class comes from the steel and heat treatment, not the dimensions, so screws of the same size and length weigh the same in 8.8, 10.9 and 12.9.

What Allen key size fits an M16 or M24 socket head cap screw?

An M16 socket head cap screw takes a 14 mm Allen key and an M24 a 19 mm key.

Is the thread of a socket head cap screw weighed at full diameter?

No. The threaded length is weighed at the pitch diameter, as in the published DIN 912 weight charts. The plain shank under the head is weighed at full diameter.

Socket Head Cap Screw (Allen Bolt) Weight Chart & Calculator

Weight of socket head cap screws — Allen bolts — to ISO 4762 and DIN 912, from M8 to M64. Pick a size and length for the weight of one screw and of the whole lot, or read it straight off the chart below. S R Forgings manufactures socket head cap screws from M16 to M64; the smaller sizes are included for reference.

Size

Length under head, mm

Quantity, pieces

0kg for the lot

Socket head cap screw weight chart, M8 to M24

Weight in kg per 1000 pieces, which is the same number as grams per piece. Plain steel, ISO 4762 / DIN 912, standard lengths for each size. Blank cells are outside the standard length range for that size.

Length, mm	M8	M10	M12	M16	M20	M24	M27
12	11.0
16	12.2	21.2
20	13.5	23.2	33.5
25	15.1	25.7	37.1	76.9
30	16.9	28.2	40.8	83.5	149
35	18.8	31.0	44.4	90.2	160
40	20.8	34.1	48.7	96.9	170	276
45	22.8	37.2	53.1	104	180	291	401
50	24.8	40.3	57.6	112	191	306	420
55	26.7	43.4	62.0	120	202	321	440
60	28.7	46.5	66.4	127	215	336	459
65	30.7	49.5	70.9	135	227	353	478
70	32.6	52.6	75.3	143	239	371	500
80	36.6	58.8	84.2	159	264	407	545
90		65.0	93.1	175	289	442	590
100		71.1	102	191	313	478	635
110			111	206	338	513	680
120			120	222	363	549	725
130				238	387	584	770
140				254	412	620	815
150				269	437	655	860
160				285	461	691	905
180					511	762	994
200					560	833	1,084

Socket head cap screw weight chart, M30 to M64

The large sizes, where weight starts to matter for freight and handling. A single M64 × 300 socket head cap screw weighs just over 10 kg.

Length, mm	M30	M33	M36	M42	M48	M56	M64
45	527
50	550	716
55	574	745	913
60	598	774	947	1,394
65	622	803	981	1,441
70	645	832	1,016	1,489	2,107
80	699	892	1,085	1,583	2,231	3,338
90	755	960	1,160	1,677	2,354	3,507	5,002
100	810	1,027	1,240	1,777	2,478	3,677	5,224
110	866	1,094	1,320	1,886	2,605	3,846	5,447
120	921	1,161	1,400	1,994	2,747	4,016	5,670
130	977	1,228	1,480	2,103	2,889	4,199	5,893
140	1,032	1,295	1,560	2,212	3,031	4,393	6,115
150	1,087	1,362	1,640	2,321	3,173	4,586	6,368
160	1,143	1,430	1,719	2,429	3,315	4,780	6,620
180	1,254	1,564	1,879	2,647	3,599	5,166	7,125
200	1,365	1,698	2,039	2,864	3,884	5,553	7,631
220				3,082	4,168	5,940	8,136
240				3,299	4,452	6,326	8,641
260				3,517	4,736	6,713	9,146
280				3,734	5,020	7,100	9,651
300				3,952	5,304	7,486	10,156

Allen bolt weight for any length

Socket head cap screws are often made to lengths outside the standard series. Every length can be worked out from three figures for its size: the weight of the head, the weight per mm of the threaded length, and the weight per mm of the plain shank. The thread length b is the ISO 4762 reference value; a screw shorter than b is threaded all the way to the head.

Size	Pitch	Head dia dk	Head height k	Allen key s	Thread length b	Head, g	Threaded, g/mm	Plain shank, g/mm
M8	1.25	13	8	6	28	7.2	0.319	0.395
M10	1.5	16	10	8	32	13.1	0.502	0.617
M12	1.75	18	12	10	36	18.9	0.728	0.888
M16	2	24	16	14	44	43.6	1.332	1.578
M20	2.5	30	20	17	52	86.7	2.082	2.466
M24	3	36	24	19	60	155.8	2.998	3.551
M27	3	40	27	19	66	226.7	3.869	4.495
M30	3.5	45	30	22	72	313.4	4.740	5.549
M33	3.5	50	33	24	78	425.0	5.821	6.714
M36	4	54	36	27	84	534.3	6.879	7.990
M42	4.5	63	42	32	96	829.5	9.415	10.876
M48	5	72	48	36	108	1243.1	12.348	14.205
M56	5.5	84	56	41	124	1982.1	16.947	19.335
M64	6	96	64	46	140	2997.3	22.272	25.253

Worked example: M24 × 100

Head: 155.8 g
Threaded length 60 mm × 2.998 g/mm = 179.9 g
Plain shank 40 mm × 3.551 g/mm = 142.1 g
Total 477.8 g per piece, or 478 kg per 1000 pieces — about 2 pieces to the kilogram

How the weights are calculated

Each weight is built up from the ISO 4762 nominal dimensions in steel at 7.85 g/cm³. The head is a cylinder of head diameter dk and height k, less the hexagon socket and the drill cone at its bottom. The threaded length is taken at the pitch diameter of the thread, and the plain shank at the nominal diameter. For M8 and for M24 upwards the results agree with the widely published DIN 912 weight charts to within about two per cent. Between M12 and M20 the published charts differ among themselves, and these figures come out a little heavier than some of them. Actual weight varies a little with head chamfers, the under-head radius and socket depth, so use these figures for estimating, freight and costing, and the weighed despatch figure for billing.

Property class makes no difference to weight: an 8.8, a 10.9 and a 12.9 screw of the same size weigh the same. Zinc plating and zinc flake coatings add too little to change the figures.

Socket head cap screws from M16 to M64

We manufacture socket head cap screws to ISO 4762 / DIN 912 in property classes 8.8, 10.9 and 12.9, from M16 up to M64 — the large sizes that are hard to find from stock. Standard lengths, longer lengths and special heads to your drawing. Black or zinc plated. Send us the size list and quantity and we will quote with weights and delivery time.

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Frequently asked questions

What is the weight of an M20 Allen bolt?: An M20 × 50 socket head cap screw weighs about 191 g, and an M20 × 100 about 313 g. Each extra 10 mm of thread adds roughly 21 g. The chart above gives every standard length.
How many Allen bolts are there in 1 kg?: It depends entirely on size and length: about 74 pieces of M8 × 20, 17 of M12 × 50, 9 of M16 × 50 and 2 of M24 × 100. The calculator shows pieces per kg for any size you enter.
Does a 12.9 socket head cap screw weigh more than an 8.8?: No. Property class comes from the steel and its heat treatment, not the dimensions, so screws of the same size and length weigh the same in 8.8, 10.9 and 12.9.
What Allen key size fits an M16 or M24 socket head cap screw?: An M16 takes a 14 mm key and an M24 a 19 mm key. The full list, from 6 mm for M8 up to 46 mm for M64, is in the dimensions table above.
Is the thread weighed at full diameter?: No. The threaded length is weighed at the pitch diameter, which is how the published DIN 912 weight charts are built and why they come out lighter than a plain round bar of the same length. The plain shank under the head is weighed at full diameter.