Yes, what can you say about the M16 thread? It is easily confused with GA3 / 8 thread which is in porcelain lamp holder.
If you have an older outdoor lighting that needs to be renovated, it is very likely that it has a lamp holder with GA3 / 8 thread that is similar to the M16.
Send us a picture / pictures and we will help you solve it.
Porcelain holders can be found in the lamp holder menu or in the menu grounded lamp parts