When selecting the best fully insulated female spade connector, it is essential to consider the wire size (mm or AWG) as well as the tab size which it will likely be connected. The width in the receptacle should match the width of the tab, and also the thickness of the tabs may vary. Common tab sizes include .110 (2.8mm), .187 (4.8mm), .205 (5.2mm), .250 (6.3mm), and .375 (9.5mm). Proper selection ensures a secure and reliable electrical connection.