In consequence of the considerable wear of the screws and nuts belonging to all gland-studs in general, it is advisable to make them all of steel. But the worm-wheels of glands are made of gun-metal, or of cast iron, and because they require to have screwed holes in their bosses, for rotation on the studs, loose screwed bushes may be provided. These can be made of steel, and keyed in the wheels, so that they can be easily removed when worn, and new bushes put in. But bushes are only necessary if the threads are very fine or shallow; the threads should be very coarse, compared with those usually adopted for stated diameters; and coarse threads for such articles will prevent the necessity for future repairs.