Home › Forum › Ask A Member › 13/16" Expansion Plugs › Re: 13/16" Expansion Plugs
I did not endorse it, I don’t do that for the online sources.
I suggest them only.
Since our suggestions failed to meet expectations, check Joe’s article and go from there.
Best,
PM T2
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Requested a quote for brass and steel expansion plugs in the better “ground” version
and in the standard version. Will let you know what they say.
In the mean time, what in the world is the Spherical Radius shown in the photo
and what do it matter as long as the diameter is correct?
It matters. The spherical radius in the design is related plug diameter to affect sealing in the hole once installed convex side out and struck with a hammer to somewhat flatten the convex surface to tighten the plug. Noted below.
Ref Wikipedia:
https://en.wikipedia.org/wiki/Core_plug
Welch plug
The Welch plug, (misnomer: Welsh plug), is a thin, domed disc, of a metallic alloy, which is pressed, convex side out, into a casting hole and against an internal shoulder.[4] Alternatively a non-ferrous metal such as brass offers improved corrosion prevention. When struck with a hammer, the dome collapses slightly, expanding it laterally to seal the hole. Other core plugs have a dish design, so that when pressed into the casting hole the tapered sides form the seal.[5]
According to Nevin Hubbard of the M.D. Hubbard Spring Company, the Welch plug was originally designed in the 1900s by the Welch brothers at the Welch Motor Car Company of Pontiac, Michigan. Hubbard claims that "at that time core holes in the engine blocks were fitted with pipe plugs. During one of these run-ins a pipe plug backed out. In order to get back on the road one of the brothers drove a quarter or half dollar into the hole. From this they developed the Welch plug, some with the help of my great grandfather Martin Hubbard. They then patented the plug and the M.D. Hubbard Spring Company became the sole manufacturer of the Welch plug for the life of the patent."[6]