Just as Boneh and Soter apply to building or demolishing a house, the ground, or an ohel, they also apply to building or demolishing an implement.[5] Therefore, one may not insert the handle of a hammer into the hammer head or a broom handle into the broom shaft. A permanent insertion is prohibited by Torah law, while a temporary insertion is forbidden rabbinically. Similarly, it is prohibited by Torah law to put together a bed or chair using nails, screws, or glue, since such attachments are full and permanent. Fixing a chair leg or table leg that has fallen off is also forbidden, as is attaching or removing a rubber chair tip or table tip (a rubber protector that goes underneath a chair leg or table leg).
If there is a possibility that people will forget it is Shabbat and end up fixing the implement, the Sages forbid moving it. For example, if a leg falls off a chair or table, one may not move the item and prop it up on another piece of furniture, because someone might see it and decide to repair it. However, if the implement would be complicated to fix, or if it had already been used in this manner before Shabbat, there is no concern that he will forget and repair it on Shabbat, so it may be moved (SA 313:8; Rema 308:16; MB ad loc. 69; SSK 20:44).
One may use implements on Shabbat whose normal usage involves screwing or unscrewing. Thus, one may screw a lid on a jar, salt shaker, or pressure cooker, put on jewelry whose ends screw together, or look through binoculars that are focused by turning a knob. Since this is the normal way of using these devices, screwing and unscrewing them is not considered a melakha. However, one may not unscrew something if it unusual to do so. For example, one may not unscrew the knob of a pot cover (SHT 313:32; MA states that the prohibition is by Torah law, while Taz maintains that it is rabbinic).
Most poskim allow adjusting the height of a lectern (“shtender”) by loosening a knob and tightening it at the desired height, as this is the normal usage and the lectern remains usable at every stage of the adjustment (Orĥot Shabbat 8:9 citing R. Shlomo Zalman Auerbach and R. Yosef Shalom Elyashiv; Yalkut Yosef 314:2).
One may adjust a baby carriage or stroller with hinges or latches from an upright position to a horizontal one and vice versa. However, if doing so involves removing screws that hold the seat in position and then screwing them back in, it is forbidden because it entails making a strong attachment that is adjusted only infrequently (SSK 28:50).
