Although these adapters are made of unmolded, high temperature plastic as shown in the photo, they are of high quality and cost $1.25 each, which is the best buy on the web. Please note that these adapters are used to fit a candelabra lamp into an intermediate socket. Also, they add about 0.6 inches to the overall length of the lamp due to the thickness of the base. All joints are well soldered, the brass is bright and crisp, and the inner insulator looks like resin-impregnated fiberglass. That dark Bakelite-like ring around the mouth is actually a strip of heat shrink tubing that smoothes the connection between the inner and outer shells. These shrouds are well soldered in two places and together with the rivets and soldered center conductor create a solid construction that is easy to tighten and forms a rigid mount. Cap-down bulbs I use one to light a modified Feit LED in an old tensor cap-up bulb. The Feit LED only consumes 7.5W replacing a 40W incandescent bulb so this particular adapter should last 25,000 hours of LED life. The fact that these adapters are assembled and soldered by hand is a testament to their ability to withstand fairly high temperatures. While I would question the feasibility, it seems they might also be suitable for adapting a 40 watt incandescent bulb into a base down configuration. However, I would not do that in the basic configuration. In such a difficult situation, I would opt for the much more expensive and less readily available ceramic adapter. Just my opinion.
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