These fasteners are often used with nuts but also often tightened into tapped holes (without nuts). They might be considered a screw, or a bolt based on the Machinery’s Handbook distinction. In practice, they tend to be mostly available in smaller sizes up to M8.
A quality assured range of machine Screws is available with us in various head and drive styles.
Drive Styles: 
Slotted, Cross Recessed Phillips and Pozi drive, Torx Drive and Hex Socket Drive apart from Tamper-Resistant special drives.
Head Styles:
Cheese head, PAN head, CSK [Countersunk] head, Truss head, Hex Head, Socket Cylindrical head, Flanged head, Low Cylindrical head, Ultra Low Profile Head, etc
Special Styles: Wing Screws, Headless Grub Screws. Eye Screws, Square Neck Dome Head, SEMS type with assembled washers, Captive type with reduced shank, 100deg CSK Screws and Ultra Low Profile Head Screws.
Thread Types:
Metric
Metric Trilobular [Taptite]
Unified.
Materials: Mild Steel, Hardened Alloy Steel, Stainless Steel grades AISI 304 and 316, Titanium Grade 2 and Brass [on order].
Finish:
Zinc Electroplated White passivation & Yellow Passivation, Stainless Steel Passivated, Zinc Black and Anodised on order.
Range – ISO Metric M3 to M16 up to 120mm length
ISO Metric Micro Series M1.0 to M2.5 up to 50mm length
Inch Series BSW 1/8″ to 1/2″ up to 4″ Length, UNC 2-56 to 10-32UNF.
These Machine Screws are manufactured with high precision to ensure quality.
Standards – DIN 84, DIN 85, DIN 912, DIN 933, DIN 963, DIN 965, DIN 7985, JIS B1111, DIN 7500, ISO 14581, ISO 14583, ISO 7380, ISO 5856, NF E 27-128 NF E 25-129.
ROHS Status:
RoHS 3 Compliant in most products
Certification: COC is provided on request and is chargeable.
Captive screws basically are specially designed to lock into position in a hole, 
enabling easy setting up and removing of the attached pieces even without the complete removal of the screw.
SEMS Screws are screws preassembled with free spinning washers. The 
assembly typically contains one plain washer and one split spring washer.
Ultra-thin head screw that are 77% thinner than conventional pan head w
hich makes possible flat external surface and contributes low-profile design and weight saving.
- PAN TORX MC Screws ISO 14583
- The Torx compatible drive is a reliable method of fixing screws.
- This drive can take more torque and does not slip. PAN Head provides a very good and tight joint.
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CSK TORX MC Screws ISO 14581
The Torx compatible drive is a reliable method of fixing screws. This drive can take more torque and does not slip.
The hex socket screw drive has a hexagonal recess and may be driven by a hex wrench, also known as an Allen wrench, Allen key or hex key, as well as by a hex screwdriver (also known as a hex driver) or bit.
They are commonly referred as Allen Screws. Tamper-resistant versions with a pin in the recess are available.