I frequently see 9g mentioned in servos. I searched the web but couldn't find any worthwhile answers. At first I thought it meant 9grams but the weight of the servo isn't 9 grams, so have to be something else.
According to Flite Test web site, the 9g reference is the weight without the wire lead. They measured one model at 8 grams rounded down. I suspect the weight also ignores the horn as well as the wire.
The article referenced on the web site calls the weight reference as a standard, which means that it more likely allows for heavier or lighter servos as long as the size of the servo matches.
If you purchase a servo for a model known to use a 9g servo, you know the hole you have to build for it to fit. If you purchase a 5g servo, it will be a different hole and you may have a 6 or 7 gram weight, but the servo fits as it should.
From a model airplane perspective...
The "9g" is supposed to mean 9 grams in weight. Each vendor has their own way to define their weight.
- with wires
- without wires
- with or without control horns
- "about the same as a competitor's 9 gram servo"
Most are not accurate.
It is not a standard for size, and has nothing to do with hole size or screw spacing