these are neeeded when using a hho system or a test pipe. they are also used to lean out your vehicle for better gas mileage._x000D_ they are very easy to install by unscrewing your O2 sensor from your exhaust then screw your sensor into the extender and then screw the two pieces back into your exhaust._x000D_ the extender has A 7/8 hex which is the same size as most O2 sensors and it makes them easier to install not like the straight sided extenders._x000D_ fits most sensors with a1/2 inch diameter tip. the size of the extenders is X 1.50 and they are 1.253 inches long and drilled out to .5175 inches. if you need more clearance you can stack them and they have a tapered seat no washer needed. Color: Silver_x000D_ Material: Iron_x000D_ Model:*1.5_x000D_ Universal For Any Thread Size Of 18mm_x000D_ Straight Bolt-On, No Modification Needed_x000D_ Very Easy To Install Package Contents:_x000D_ 1PCS X oxygen sensor Only the above package content, other products are not included._x000D_ Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm. _x000D_ _x000D_ _x000D_ _x000D_ _x000D_ _x000D_ _x000D_