The magnetic bit holder is an indispensable accompaniment to any drill driver. It consists of a hexagonal steel bar, one end of which grips the chuck. The other end comes with a chrome steel cylinder into which any screwdriver bit will slot. A small magnet also prevents the bit from dropping out. The new locking bit holder feature two magnets to maximize magnetic transfer and holding power to the fastener and prevent drops. As with all SHOCKWAVE™ Impact Duty Accessories, each bit holder features an optimized SHOCK ZONE™ geometry to provide up to 30X longer life and absorb 3X more torque to prevent breakage. Work Environment a lighter weight mag drill is preferred if you are working high up in the air, etc. Space Limitations – If you are working in tight spaces a low-profile mag drill may be ideal, such as: The Hougen HMD130 Mag Drill or the Fein JMC Magforce 90 Mag Drill. Our SHOCKWAVE™ Impact Duty™ Magnetic Bit Holders are engineered for extreme durability and up to 30x life. The MILWAUKEE magnetic bit holders are made from proprietary steel, heat treated to control hardness. The SHOCKWAVE™ magnetic bit holders feature a powerful magnet, providing you with a secure grip and unyielding bit engagement . Each bit holder has a 2-piece construction for optimal assembly in abusive applications. Our SHOCKWAVE™ Impact Duty™ Magnetic Bit Holders have a C-ring to retain the insert bit and can now be used with Milwaukee SHOCKWAVE™ Impact Duty Insert Magnetic Nut Drivers (¼”, 5/16”, ⅜”, 7/16”, ½”). A "bit-holder" will often be magnetized to hold the bit in (and incidentally holding the screw as well) while the other two can be, but it's not as common. A "hex bit socket" or "nut driver" is probably more durable than a "bit holder" if it matters to you, for example if you're using a high torque impact driver.