Made of alloy steel, hex head grub screw cup point socket.
Often used for holding a pulley, gear, or other parts from turning relative to a shaft.
 

• Drive Type: Hex Socket; Head Style: Cup Point; Material: Alloy Steel
• Package Content: 50(+/-2%) x Grub Screw; Product Name: Grub Screw; Thread Size: 4# x 3/8" (D*L)
• Weight: 13g; Head Size: 2mm/0.08"
• Hex Key Size: 1.5mm/0.06"; Main Color: Black
• Thread Count: 40; Grade: 12.9

Drive Type: Hex Socket; Head Style: Cup Point; Material: Alloy Steeluxcell