The back of the Bakelite case for a typical Triplett VOM or VTVM is attached to the front by four machine screws.
The screws are accessed through deep wells molded into the back of the case. While there are small feet molded into the Bakelite casting, …
… Triplett also provided rubber feet that fit into the holes in the back.
The trade name for these little rubber frobs seems to be “push-in bumpers”.
The Triplett 639-N “barn-door” case for their 630 series meters also has holes for rubber bumpers. I don’t know if the cases originally came with feet installed or if you were expected to remove the feet from your meter and install them in the case.
The feet are almost inevitably missing from any used Triplett meter that I have acquired. This Model 800 VOM is one of the few exceptions.
The leftmost foot is from the Triplett 800 VOM. The one immediately to its right is one of the feet that came with my new-in-box Triplett 630-APLK Type 5 VOM. The foot from the 800 appears to be the same shape as the new foot from the 630-APLK, but it is slightly smaller in diameter. The previous owner had wrapped the feet on the 800 with a layer of masking tape to hold them in place.
I guess the feet shrink a bit over time, fall off the meter, and are discarded or lost. I think that is why used meters rarely have their feet.
This leaves us with the problem of finding rubber bumpers to use as replacements for the missing meter feet. I haven’t been able to find exact replacements. The original Triplett bumpers (the two on the left) are a fairly soft rubber (at least when new) and have a taper at the end to make it easier to insert them into the mounting hole.
The Triplett feet from the 630-APLK are 0.3125" (5/16") ID , 0.3125" (5/16") stem height, and 0.450" (29/64") OD. The end of the stem tapers to about 0.260" over a length of about 0.090". The hole through the center is 0.125" (1/8") in diameter.
I’ve measured the mounting hole diameter as 0.300” inch. You need to size the stem of the bumper a little larger, so that it compresses when inserted into the mounting hole.
The middle bumper is from Schaff Piano Supply Co., courtesy of Fred Scoles. It is their No. 357 rubber bumper, stem diameter 11/32”, head diameter 7/16”. As Fred wrote in a post on the Antique Radio Forum, they fit the holes in the back of Triplett cases very well.
The last two bumpers are from McMaster-Carr. The fourth bumper from the left is their number 9544K23, for 9/32” ID, 1/4” stem height, 7/16” OD, SBF Rubber. It is close to the right style, but the stem diameter is 1/16” too small. A few wraps of masking tape fixes that problem, but it would be nice to be able to source a similar part with a slightly larger stem diameter.
The rightmost bumper is McMaster-Carr’s number 9544K34, for 5/16” ID, 1/4” stem height, 5/8” OD, SBR Rubber. They are a harder rubber than the Schaff #357 bumpers, so despite having a smaller diameter stem, they still grip the sides of the mounting hole very well. Unfortunately they are both too large in outer diameter and in thickness to look good on the meter.
I've just noticed that McMaster-Carr has a larger selection of push-in bumpers now. I've ordered some of their number 9544K553, for 5/16" ID, 1/2" stem height, 7/16" OD, SBR Rubber. These should fit well.
Also, prior to Fred sending me the Schaff #357 bumpers, I hadn't thought a 11/32" soft rubber stem would fit the holes. So I've also ordered McMaster-Carr's number 9310K12, for 11/32" ID, 13/16" high stem, SBR Rubber. The OD is much too large, but I may be able to cut it down.
I’ve searched other suppliers for something closer to the style and size of the Triplett OEM feet, but I haven’t found anything closer than these.
Here’s one of my Triplett 630-NA’s with the Schaff #357 bumpers. (Thanks Fred!)
Here is my 630-APLK Type 5 with the Triplett feet.
Update:
The stem of the number 9310K12, for 11/32" ID, 13/16" high stem, SBR Rubber bumpers is too large to fit. If it was half the length it would probably fit, so I guess the stem could be cut down. But the OD of the head is still too big as well.
The number 9544K553, for 5/16" ID, 1/2" stem height, 7/16" OD, SBR Rubber bumpers have too long a stem to easily fit in the mounting hole, and the bumper is too thick. I didn’t notice the specs that said the height of the bumper, exclusive of the stem, is 7/16”.
So, I think the best options are either the Schaff No. 357 bumpers ...
… or the McMaster-Carr number 9544K23, for 9/32” ID, 1/4” stem height, 7/16” OD, SBF Rubber bumpers with a few wraps of masking tape on the stem.