grease fittings are permanently installed by a threaded connection, leaving a nipple connection that a grease gun attaches to. the pressure supplied by the grease gun forces a small captive bearing ball in the fitting to move back against the force of its retaining spring. the arrangement is thus essentially a valve that opens under pressure to allow lubricant to pass through a channel and be forced into the voids of the bearing. when the pressure ceases, the ball returns to its closed position. the ball excludes dirt and functions as a check valve to prevent grease escaping back out of the fitting. the ball is almost flush with the surface of the fitting so that it can be wiped clean to reduce the amount of debris carried with the grease into the bearing. the convex shape of the fitting allows the concave tip of the grease gun to seal against the fitting easily from many angles, yet with a sufficiently tight seal to force the pressured greased to move the ball and enter the fitting, rather than simply oozing past this temporary annular (ring-shaped) seal. grease fittings are commonly made from zinc-plated steel, stainless steel, or brass. since the 1920s, the ever-growing dissemination of sealed bearings throughout the manufacturing industries has made the use of grease fittings less common. sealed bearings are lubricated for life at the factory, and are sealed such that the lubricant is not lost or dirtied. however, grease fittings are far from obsolete, and much new machinery is built with them every year (e.g., tractors, lawnmowers, automatic pool covers, industrial plant, and still a few car and truck parts), because as long as maintenance is even minimally attended to (via occasional lube jobs where new grease is pumped into the bearing), this type of bearing and lubrication setup is cost-effective, simple, and long-lasting. however, total neglect of maintenance shortens lifespan. grease fittings are rarely found on today's consumer goods, appliances, or cars, because maintenance-free products have more sales appeal to the general public. they are still commonly used on industrial, agricultural, and mining equipment where shaft diameters exceed 20 millimeters, as well as electric motors larger than 5 kilowatts. one of the reasons for this is that commercial users have plans and enforcement for lubricating schedules, so the expense of sealed bearings may be unnecessary. for example, in ship or power plant mro, the management will ensure and document that an employee does the lubrication rounds as needed, whereas individual consumers often ignore maintenance needs. in commercial use, as long as the lubrication rounds are being added to the workload of an already-needed employee, thus not expanding the payroll, this is the less expensive route. grease fittings are commonly found on marine engines. besides providing fresh lubrication, pumping grease into a grease fitting on a boat motor or lower unit expels moisture that would otherwise cause corrosion.[2] 黄油嘴fittings? ? 公制螺纹直通/45度/90 美制螺纹直通/45度/90度 英制螺纹直通/45度/90 metric fittings npt/unf/unc threads fittings bsp threads fittings ? 螺纹 长度 对边的大小 m6x1 21mm 10mm m8x1 21mm 10mm m8x1.25 21mm 10mm m10x1 21mm 10mm m10x1.5 21mm 11mm m12x1 23mm 12mm m12x1.25 23mm 12mm m12x1.75 23mm 12mm m14x1 30mm 14mm m14x1.5 30mm 14mm m16x1 34mm 17mm m16x1.5 34mm 17mm m18x1.5 36mm 19mm 螺纹 长度 对边的大小 形式 1/4-28" 19mm 7mm unf 5/16-24" 21mm 10mm unf 3/8-24" 21mm 11mm unf 7/16-20" 25mm 12mm unf 1/2-20" 30mm 14mm unf 9/16-18" 34mm 15mm unf 5/8-18" 25mm 17mm unf 5/16-18" 21mm 8mm unc 3/8-16" 21mm 10mm unc 1/8-27" 23mm 11mm sae 1/4-18" 25mm 14mm sae 螺纹 长度 对边的大小 bsp 1/8-28” 21mm 10mm bsp 1/4-19” 25mm 14mm bsp 3/8-19” 21mm 11mm bsp 3/16-24” 19mm 8mm