✔ Meets/Exceeds: DIN 912
✔ Screw head style: socket cap, head diameter: 5.5 mm, head height: 3 mm
✔ Screw drive system: internal hex drives, also known as hex socket , hex size: 2.5 mm
✔ M3 x 40 means : Metric screws, Thread diameter size 3 mm, Thread length 40 mm

[ Sizes ]-----[ Thread Length ]------[ Total Length ]
M3 x 40----------40mm/1.57"---------43mm/1.69"
M3 x 45----------45mm/1.77"---------48mm/1.89"
M3 x 50----------50mm/1.97"---------53mm/2.09"
M3 x 55----------55mm/2.17"---------58mm/2.28"
M3 x 60----------60mm/2.36"---------63mm/2.48"

[ Package Contains ]
M3 x 40------------10 Pcs
M3 x 45------------10 Pcs
M3 x 50------------10 Pcs
M3 x 55------------10 Pcs
M3 x 60------------10 Pcs
Hex Key --------1 Pcs

[ About Internal Hex Drives ]
Internal Hex drives, also known as Hex Socket Drives , have a hexagonal hole in the center that requires an Allen key, also known as a hex key or Allen wrench
[ About Socket Cap Head ]
Socket Cap Head , also known as Allen head , have a recessed drive, and are commonly used when there is not enough clearance for a conventional wrench or socket. They are fastened with an Allen wrench, which is also called a hex wrench or hex key