RS Pro Extension Bars. The RS Pro extension bars are designed to add length when used with ratchets or breaker bars. These quality extensions Improves the torque delivery when loosening and tightening fasteners. Exceptional strength and durability offers long life usage. RS stock number and size. < 912-5414') 912-5414/: in drive x 50 mm < 912-5423') 912-5423/: in drive x 100 mm < 912-5426') 912-5426/: 3/8 in drive x 75 mm < 912-5420') 912-5420/: in drive x 75 mm < 912-5439') 912-5439/: in drive x 250 mm. Features and Benefits. Made from Chrome vanadium Matt finish Adds length to access hard-to-reach fasteners Knurled bands offer a nonslip grip for turning loosened fasteners by hand Detent notches in drive ends lock onto ratchets and breaker bars Strong and durable. Application Information. Designed to be used by professionals in workshops and automotive applications