If you take a good look at a standard SIM, you'd see that the chip or contact area doesn't cover much space and that makes SIM very customizable. From micro to nano, then maybe Biro. The conventional SIM takes up alot of plastic so you could come up with biro SIM someday, maybe smaller than nano.


1. SIM Cutter

This is the most convenient and trusted way to get a SIM cut, well marred like a cool hair cut. They are lots of SIM cutter variants (Nano and Micro cutter) out there in the market, it's left for you to get one.

• How to used a SIM cutter
Kindly place the SIM in the slot, press down the handle of the cutter and woah! Your SIM cut is ready. An advantage of using an engineered cutter is that the left over plastic can be used as an Adapter.


2. Craft Knife

You are going to be using a craft knife and not a kitchen knife. My first paragraph is to ensure you're reading this post vehemently without skipping any word. You can also use your K Knife if there are no C knife's available, but please be careful in cutting so you won't damage the chip area.

• How to Carve Out SIM using Craft Knife
You'll need a sample SIM in order for you to cut out your preferred SIM. You can borrow from a friend or college or rather download and printout SIM templates online and use it for cutting.


3. Scissors

This is probably the quickest and safest tool after the SIM cutter. Get a sample SIM, place it on it the standard SIM, then trace it with the scissors cutting through the plastic and you're done with the SIM cut.
If you're not too sure about the area, you can stencil before cutting through with scissors.


Disclaimer:
Performing this DIY could be nerve bombing and disastrous (I'm joking about disastrous). Perform all tips at your own risks.

Note:
You can make a couple of bucks from these tips.


An Excerpt from:
https://gklited..com/2017/01/how-to-cut-your-nano-and-micro-sim.html?m=1

Use sim cutter to be on a safer side
Nice topic @ OP