Philips Sonicare - Head shaft screw and washer replacement

Hello.

I just took apart my Philip Sonicare HX680C toothbrush in order to tighten the head shaft screw, as it has been very loose lately - common complaint. To my surprise, however, when I opened the toothbrush, the screw and washer that are supposed to be there have seemingly vanished entirely. With my micrometer nowhere to be found, would anyone be able to tell me what the appropriate dimensions of the screw and washer? Thanks!