Is it a fuse? Nope. A grid Leak

I should note that they made Carborundum detectors in similar tubes, but with an adjustable nut or screw on the end so you could vary the pressure on the Carborundum xtal.
Carborundum detectors also required a voltage on them to operate . IIRC it was like 1.5 to 3VDC.

When restoring a radio and it uses a grid leak in a standard fuse size glass, just heat the ends of a fuse and pull the element out.
 Clean up the ends and glass and put a resistor in the glass and glue the ends back on. Most ends will have a small hole in the end where the fuse wire came through the cap and was soldered on to the end.

 Not 100% authentic but will snap in and out. However the size of the glass or other material tube did vary in diameter. Sometimes the holders did look like an odd size fuse holder.

BTW grid leaks came in a few casing sizes, and some that even had the big "solder blobs" on the ends like early Atwater Kent resistors did. Just more info to add to the confusion.

I have a couple of these in my parts stash. However, I never knew there were glass ones. I know now though. Thanks Frank! 

Or just replace with a Resistor of same Value .

A few decades ago when I was working for a wholesaler a customer from one of the shops came in and asked for a "fuse", and handed the "bad" one to me.

Just because it looks similar to a fuse- being in a glass tube with ends that snap into a fuse holder type connector does not mean it's a fuse.

In reality this one was a grid leak resistor.

He had tested on low ohms and thought it was bad. It likely read in several megohms.


So if you find something that looks similar to a fuse- and some of these had solder on each end- does not mean it is a fuse. It may be a grid leak. Typically they can measure from 1 meg to 20 meg.
 Most were in glass tubes the same size aa a fuse or larger. They are getting hard to find also.( Some are also in ceramic type tubes, and I even saw one in a Bakelite tube too).
 Sometimes they will have the original label on them saying "Grid Leak XXX ohms". 

(Now remember if you must replace a grid leak, remember to replace the drip pan also.   )