There is not an absolute answer – but in most cases, the answer is YES if the attachment is going over the collet nut or chuck. Because once the attachment is over those, you can't access the collet nut or the chuck. You have to install the accessory into the tool, then connect the attachment. Examples of some of the attachments that you should insert the accessory before completing the attachment connection are the Shaper Router Table (because it's hard to see), and guides that help manage depth like the Cutting Guide or Circle Guide.