A short while ago I acquired this circa 1964 Hamilton Dateline T-477 Thin-o-matic, and was wondering what movement it housed in the one-piece case.

Well, the day has arrived for the me to delve into the inner sanctum of this mystery. My crystal lift tool finally arrived, and I set forth, not without a little trepidation. I needn’t have worried, the tool worked a treat, with the crystal needing only a smidgeon of compression in order to lift cleanly out of the one-piece case. Below you can see that the Claw has done its job…

Alas, it is not a Buren
micro rotor as I had hoped. The movement is in fact a Hamilton Grade 624 17 jewel full-rotor (Swiss). The movement is removed easily from the case by turning the crown to a position where the two-piece stem slides apart…

Here is the inside of the golden sarcophagus. French scholars are even now working feverishly to decipher these strange hieroglyphs…

I’ve taken quite a liking to this little Thin-o-matic. The crystal slipped back in easily and the watch is once again whole, none the worse for the experience. The mystery has been solved.

A word on two-piece, or split stems. There are two types of split stems, the male/female type, in which the crown and outer stem piece pull apart to allow the movement to be extracted from the case. The other type, as found in both Hamilton watches discussed here, is the keyed type wherein the stem parts are keyed together to operate normally, but when aligned (turned) to face the front of the case, allow the outer and inner stem pieces to slip apart. Below is a rough drawing of what a keyed split stem looks like when aligned properly for extraction of the movement from the case.

This type of stem can be identified readily by having a close look, perhaps through a loupe, after the crystal has been removed from the one-piece case. The crown and outer stem piece remain in the case.

Fortified by my success in removing the crystal of my Hamilton Thin-o-matic, I proceeded to attack my other one-piece cased Hamilton. I don’t know much about this one. I expect it is from the 1960’s and is quite a good looker, with a very clean linen-textured silver dial.

This is a very slim watch. The 10K RGP case (Star Watch Case Co) is only 4.50mm ( the crystal adds another 3.20mm, and the diameter of the case is 33mm). It’s a manual-wind. The pic below illustrates the slimness…

Here you see the poor little watch about to be eaten by the Claw! Each prong of the crystal lift tool grasps the acrylic crystal at it’s edge. (Note: in actually removing the crystal I first wrapped it’s edge in masking tape with the aim of protecting it from being marked by the tool, (this may not be necessary, but did not seem to hinder the tool in operation).

For anyone who has not seen a crystal lift tool in any detail before, here is an general shot of it. The knurled knob at the left end of the tool controls the expansion and contraction of the prongs. This particular tool will handle crystals of sizes 12mm – 37mm.

Here’s a close up of the crystal in the prongs. As with the Hamilton Thin-o-matic, only moderate compression of the crystal was required to allow it to be extracted from the watch case.

The three major components of the watch – one-piece case, dial/movement, and crystal…

..and here is the movement. This is a manual-wind Hamilton Grade 639, 17 jewels unadjusted. I had wondered what was inside this watch since obtaining it about 2 years ago. Now I know.

In order to replace the crystal, it is placed on the plate supplied with the tool, as illustrated below. The purpose of this plate is to allow the tool to grasp the crystal at it’s edge, whilst allowing a small amount of the crystal to protrude below the prongs, so that it can be inserted into the watch case. The silver metal section on the right of the plate is adjustable to fit around different sized crystals, and can be revolved 180 degrees to cater for very small crystals. The tool’s prongs rest on these silver plates whilst grasping the crystal, leaving approx. half a mm to protrude below.

Once the crystal is grasped and compressed by the tool, it is inserted back into the watch case, and the tension of the tool is then released. The crystal expands, seating itself into the case. Pressure can then be applied around the edges of the crystal to ensure it has seated correctly. In this case I heard a distinct “click” as the crystal seated. The job was then done.

Copyright 2000 Paul Delury