Flat Head Screws Manufacturer in India | Countersunk Flat Head Screws

Overview

Countersunk Flat Head Screws & Flat Head Machine Screws: Manufacturer & Exporter

A flat head screw sinks into a cone-shaped countersink and finishes flush with the surface. Nothing stands proud to snag, and the cone centres the part on the screw.

Exotic Alloy manufactures flat head screws in Mumbai, India, for electronics, enclosure, machinery, hardware and furniture makers. We stock across India and export to Japan, South-East Asia, the Gulf, Europe and the Americas. Heads are cold formed with the slot or recess, and threads are rolled.

Two angles, one idea

Inch flat heads to ASME B18.6.3 have an 82° head; metric countersunk screws to ISO 2009 (slotted, formerly DIN 963) and ISO 7046 (cross recessed, formerly DIN 965) have a 90° head. Hex socket flat heads like the one in our photo are covered on our countersunk bolts page; for a raised top see oval head screws.

ASME B18.6.3 ISO 2009 / ISO 7046 82° & 90° Slotted, cross, socket A2 / A4 stainless

Flat head screw at a glance

Head: Countersunk cone with a flat top
Angle: 82° inch (ASME); 90° metric (ISO)
Length: Overall, head included
Drives: Slot, Phillips, Pozidriv, hexalobular, hex socket
Sheet: At least as thick as the head
Related: Countersunk screws, oval head, countersunk bolts

ISO 7046-1 M6 × 20 cross recessed flat head, drawn to scale from the ISO head dimensions. The dashed lines show the theoretical sharp-edged 90° cone; the real head edge is slightly smaller. The length includes the head; threads and recess simplified.

Specification

Flat Head Screw Specification

The range we manufacture and supply.

StandardsASME B18.6.3; ISO 2009 (ex DIN 963); ISO 7046-1 / -2 (ex DIN 965); ISO 14581; ISO 10642

Size rangeNo. 0 to 1/2″; M1.6–M10 (larger sizes to drawing)

Head angle82° inch; 90° metric; 100° and undercut heads to order

ThreadUNC / UNF; metric coarse 6g, fine to order

DriveSlotted; Phillips (H); Pozidriv (Z); hexalobular; hex socket

GradesA2-70, A4-70; steel 4.8 and 8.8; brass

FinishPlain or passivated stainless; zinc plated or black steel; plain or nickel brass

LengthOverall, including the head

CertificationMill certificate; EN 10204 3.1; PMI for stainless

PackingBoxes of 100 to 1000, bulk cartons, kits

82° vs 90°

82° or 90°? Matching Head and Countersink

The most common flat head mistake is an inch screw in a metric countersink, or the other way round.

Same head diameter, drawn to scale. With matching angles the head bears on the whole cone. An 82° head in a 90° countersink rises about 0.3 mm and bears only near the shank; a 90° head in an 82° countersink bears only on its edge.

Screw	Head angle	Countersink tool	Typical standards
Inch machine screw	82°	82°	ASME B18.6.3, ASME B18.3 (socket)
Metric screw	90°	90°	ISO 2009, ISO 7046, ISO 14581, ISO 10642
Thin-sheet inch screw	100°	100°	ASME B18.6.3 100° heads (to order)

Dimensions

Flat Head Screw Dimensions

ISO countersunk flat heads from M1.6 to M10 at the same scale, cross recess top view and 90° profile; outlines simplified.

Size	P	d_k theor. max	d_k actual max / min	k max	n slot nom (ISO 2009)	t slot min (ISO 2009)	Recess ISO 7046-1	m ≈ H / Z
M1.6	0.35	3.6	3 / 2.7	1	0.4	0.32	0	1.6 / 1.6
M2	0.4	4.4	3.8 / 3.5	1.2	0.5	0.4	0	1.9 / 1.9
M2.5	0.45	5.5	4.7 / 4.4	1.5	0.6	0.5	1	2.9 / 2.8
M3	0.5	6.3	5.5 / 5.2	1.65	0.8	0.6	1	3.2 / 3
M3.5	0.6	8.2	7.3 / 6.94	2.35	1	0.9	2	4.4 / 4.1
M4	0.7	9.4	8.4 / 8.04	2.7	1.2	1	2	4.6 / 4.4
M5	0.8	10.4	9.3 / 8.94	2.7	1.2	1.1	2	5.2 / 4.9
M6	1	12.6	11.3 / 10.87	3.3	1.6	1.2	3	6.8 / 6.6
M8	1.25	17.3	15.8 / 15.37	4.65	2	1.8	4	8.9 / 8.8
M10	1.5	20	18.3 / 17.78	5	2.5	2	4	10 / 9.8

ISO 2009 (slotted) and ISO 7046-1 (cross recessed) countersunk flat head screws, product grade A, mm. H = Phillips, Z = Pozidriv.

Size	A head dia. max / min	H head height max / min	J slot width max / min	T slot depth max / min	Threads UNC / UNF
No. 0	.112 / .096	.035 / .026	.023 / .016	.015 / .010	80 (UNF)
No. 1	.137 / .120	.043 / .033	.026 / .019	.019 / .012	64 / 72
No. 2	.162 / .144	.051 / .040	.031 / .023	.023 / .015	56 / 64
No. 3	.187 / .167	.059 / .047	.035 / .027	.027 / .017	48 / 56
No. 4	.212 / .191	.067 / .055	.039 / .031	.030 / .020	40 / 48
No. 5	.237 / .215	.075 / .062	.043 / .035	.034 / .022	40 / 44
No. 6	.262 / .238	.083 / .069	.048 / .039	.038 / .024	32 / 40
No. 8	.312 / .285	.100 / .084	.054 / .045	.045 / .029	32 / 36
No. 10	.362 / .333	.116 / .098	.060 / .050	.053 / .034	24 / 32
No. 12	.412 / .380	.132 / .112	.067 / .056	.060 / .039	24 / 28
1/4″	.477 / .442	.153 / .131	.075 / .064	.070 / .046	20 / 28
5/16″	.597 / .556	.191 / .165	.084 / .072	.088 / .058	18 / 24
3/8″	.717 / .670	.230 / .200	.094 / .081	.106 / .070	16 / 24
1/2″	.815 / .765	.223 / .186	.106 / .091	.103 / .065	13 / 20

ASME B18.6.3 82° flat heads for machine screws, slotted, inches. A max is the theoretical sharp-edged diameter.

Size	M recess dia. ref	R recess depth ref	N recess width ref	Phillips driver	G gaging dia.	F protrusion max / min
No. 0	.062	.035	.014	PH 0	.078	.026 / .016
No. 1	.070	.043	.015	PH 0	.101	.028 / .016
No. 2	.096	.055	.017	PH 1	.124	.029 / .017
No. 3	.100	.060	.018	PH 1	.148	.031 / .018
No. 4	.122	.081	.018	PH 1	.172	.032 / .019
No. 5	.148	.074	.027	PH 2	.196	.034 / .020
No. 6	.168	.094	.029	PH 2	.220	.036 / .021
No. 8	.182	.110	.030	PH 2	.267	.039 / .023
No. 10	.198	.124	.032	PH 2	.313	.042 / .025
No. 12	.262	.144	.035	PH 3	.362	.045 / .027
1/4″	.276	.160	.036	PH 3	.424	.050 / .029
5/16″	.358	.205	.061	PH 4	.539	.057 / .034
3/8″	.386	.234	.065	PH 4	.653	.065 / .039
1/2″	.418	.265	.069	PH 4	.739	.081 / .049

ASME B18.6.3 Phillips recess (reference) and protrusion gauging, inches: with the countersink at the gaging diameter G, the head top stands F above the surface.

Countersinks

Countersinks & Sheet Thickness for Flat Head Screws

Size	Countersink Ø flush top, 90°	Depth = min. sheet k	Clearance hole ISO 273 medium
M1.6	3.6	1	1.8
M2	4.4	1.2	2.4
M2.5	5.5	1.5	2.9
M3	6.3	1.65	3.4
M3.5	8.2	2.35	3.9
M4	9.4	2.7	4.5
M5	10.4	2.7	5.5
M6	12.6	3.3	6.6
M8	17.3	4.65	9
M10	20	5	11

Our calculation from the ISO head: cut to the theoretical diameter, the flat top sits flush and a narrow ring of countersink shows round the slightly smaller real edge.

The material must be at least as thick as the head. In thinner sheet the countersink cuts right through, the hole edge becomes a knife edge, and the head can pull through or work loose.

Size	Flat head ISO 2009 slot depth t min	Raised head ISO 2010 slot depth t min
M1.6	0.32	0.65
M2	0.4	0.8
M2.5	0.5	1
M3	0.6	1.2
M3.5	0.9	1.4
M4	1	1.6
M5	1.1	2
M6	1.2	2.4
M8	1.8	3.2
M10	2	3.8

A flat head has room for only a shallow slot; the raised (oval) head of ISO 2010 allows a deeper one (mm).

Tap drills

Threads & Tap Drills for Flat Head Machine Screws

UNC and UNF threads for every inch size, with the drill for about 75 % thread. No. 0 is made in UNF only.

Size	Thread	Tap drill 75 % thread	Thread	Tap drill 75 % thread
No. 0	–	–	#0-80	3/64″ (0.0469″)
No. 1	#1-64	#53 (0.0595″)	#1-72	#53 (0.0595″)
No. 2	#2-56	#50 (0.0700″)	#2-64	#50 (0.0700″)
No. 3	#3-48	#47 (0.0785″)	#3-56	#45 (0.0820″)
No. 4	#4-40	#43 (0.0890″)	#4-48	#42 (0.0935″)
No. 5	#5-40	#38 (0.1015″)	#5-44	#37 (0.1040″)
No. 6	#6-32	#36 (0.1065″)	#6-40	#33 (0.1130″)
No. 8	#8-32	#29 (0.1360″)	#8-36	#29 (0.1360″)
No. 10	#10-24	#25 (0.1495″)	#10-32	#21 (0.1590″)
No. 12	#12-24	#16 (0.1770″)	#12-28	#14 (0.1820″)
1/4″	1/4-20	#7 (0.2010″)	1/4-28	#3 (0.2130″)
5/16″	5/16-18	F (0.2570″)	5/16-24	I (0.2720″)
3/8″	3/8-16	5/16″ (0.3125″)	3/8-24	Q (0.3320″)
1/2″	1/2-13	27/64″ (0.4219″)	1/2-20	29/64″ (0.4531″)

Number, letter and fractional drills with their diameters in inches.

Calculator

Flat Head Flush-Fit Calculator

Enter the countersink diameter and the sheet thickness. See where the head top will sit, how deep the countersink goes and whether the sheet is thick enough.

Screw & countersink

Screw

Size

Countersink dia., mm

Sheet thickness, mm

Our calculation. Metric: head top = (theoretical head diameter − countersink diameter) ÷ 2 for a 90° countersink. Inch: from the ASME gauge values, F − (countersink − G) ÷ (2 tan 41°). The countersink resets to the flush value when you change size.

Result

0.00

mm head top above surface

3.30

mm countersink depth

Flush countersink:Ø 12.6 mm

Head dia. (actual):10.87–11.3 mm

Drive:cross recess 3, slot 1.6 mm

Hole:6.6 mm clearance

Materials

Flat Head Screw Materials & Grades

Material	Class	Finish	Best for
A2 stainless (304)	A2-70	Plain, passivated	Electronics, enclosures, general use
A4 stainless (316)	A4-70	Plain, passivated	Marine, food and chemical equipment
Carbon steel	4.8 (ISO 7046-1), 8.8 (ISO 7046-2)	Zinc plated, black	Machinery and dry assemblies
Brass	–	Plain, nickel	Electrical and decorative parts

Stainless A2

304 · 305

The grade in the photo; 305 heads well cold.

304 305

Stainless A4

316

For salt, chlorides and cleaning agents.

316 316L

Carbon steel

4.8 · 8.8

Economical machine screws.

1018 1035

Brass

Cold-heading brass

Conductive and non-magnetic.

C26000 C27000

Manufacturing

How Our Flat Head Screws Are Made

1

Wire

Stainless, steel or brass wire, certified by heat or lot.

2

Cold heading

Cone and recess formed together at 82° or 90°; slots punched or sawn.

3

Thread rolling

UNC / UNF or metric threads rolled to the head.

4

Heat treatment

For 8.8 steel; stainless and 4.8 as formed.

5

Finishing

Passivation, zinc, black oxide or nickel.

6

Inspection

Head angle, diameter, flushness and recess checked.

Applications

Where Our Flat Head Screws Are Used

Electronics

Flush covers, chassis and heat sinks.

Enclosures & racks

Panels and rails that must slide past each other.

Hinges & hardware

Hinge leaves that close flat over the screw heads.

Machinery

Guides, wear strips and slides with nothing standing proud.

Marine fittings

A4 flat heads on deck plates and trim.

Furniture

Knock-down fittings with flush heads.

Quality & testing

Flat Head Screw Inspection & Certification

Check	Method	Applied to
Head angle & flushness	Protrusion gauge (F at G) / countersink gauge	Every lot
Head diameter	Micrometer: A / d_k	Every lot
Slot / recess	Slot gauges; recess penetration gauge	Every lot
Thread	GO / NO-GO ring gauges	Every lot
Length	Overall, head included	Every lot
Material	PMI / chemical analysis	Stainless and brass lots

Every shipment includes

Mill certificate with heat number
Dimensional report
Lot number on every box

On request

EN 10204 3.1 certificate
Salt spray test for plated lots
Count-checked kits and labels

FAQ

Flat Head Screw Questions, Answered

A flat head screw has a cone-shaped countersunk head with a flat top that sits flush with the surface. Inch flat head machine screws are made to ASME B18.6.3 with an 82 degree head; metric countersunk screws have a 90 degree head and are made to ISO 2009 (slotted), ISO 7046 (cross recessed), ISO 14581 (hexalobular) and ISO 10642 (hex socket).

Inch flat head screws to ASME B18.6.3 are 82 degrees; metric ISO countersunk screws are 90 degrees. Match the countersink to the screw: an 82 degree head in a 90 degree countersink stands proud and bears only near the shank, and a 90 degree head in an 82 degree countersink bears only on its top edge.

Over the whole screw, from the flat top of the head to the end, because the head sits inside the part. An M6 × 20 countersunk screw is 20 mm long including its 3.3 mm head.

For metric screws, cut the 90 degree countersink to the theoretical head diameter: 6.3 mm for M3, 9.4 mm for M4, 10.4 mm for M5, 12.6 mm for M6, 17.3 mm for M8 and 20 mm for M10. For inch screws, cut the 82 degree countersink to the maximum head diameter A, for example 0.362 in for No. 10. Our calculator shows where the head will sit for any countersink.

Both have the same countersunk cone. The flat head stops at a flat top that finishes flush; the oval head adds a raised dome. For ASME No. 10 the flat head is up to 0.116 in high and the oval head up to 0.176 in in total.

For ISO 7046 cross recessed screws: recess size 0 for M1.6 and M2, 1 for M2.5 and M3, 2 for M3.5 to M5, 3 for M6 and 4 for M8 and M10. For ASME Phillips flat heads: PH 0 for No. 0 and 1, PH 1 for No. 2 to 4, PH 2 for No. 5 to 10, PH 3 for No. 12 and 1/4 in, and PH 4 for 5/16 to 1/2 in.

At least as thick as the head height, so the countersink does not cut right through and leave a knife edge: 3.3 mm for M6 and 2.7 mm for M5, for example. For thinner sheet use a dimpled hole, a countersunk washer or a 100 degree head.

Most often A2 (304) and A4 (316) stainless steel, steel in property class 4.8 (the class in ISO 7046-1) or 8.8, zinc plated or black, and brass. The screw in our photo is a stainless hex socket flat head screw.