Apparatus (88) for mounting a nut plate (4) on an aircraft part and then masking the nut plate during painting of the aircraft part (6) containing the nut plate (4), which apparatus (88) comprises: (i) the nut plate (4); (ii) a first bore (10) which extends through the nut plate (4); (iii) a masking formation (8) which is made of a rigid plastics material; (iv) a second bore (52) which extends through the masking formation (8); and (v) a mandrel (68) which is made of a flexible material and which extends through the first and second bores (10, 52), and the apparatus (88) being such that: (vi) the masking formation (8) comprises a body portion (14), a masking portion (16) which is positioned at one end of the body portion (14) and which extends radially outwardly beyond the body portion (14), and a skirt portion (20) which is positioned at a periphery (22) of the masking portion (16) and which extends from a first face (24) of the masking portion (16) and away from the body portion (14); (vii) the body portion (14) extends from a second face (24) of the masking formation (8); and (viii) the mandrel (68) has a first portion (70) of a first diameter which locates in the first and second bores (10, 52), and a second portion (72) which is of a second and smaller diameter and which is for locating the apparatus (88) during the mounting and then for being pulled to remove the mandrel (68) from the remainder of the apparatus (88) after the painting.