To create your own linetype in AutoCAD is actually very easy. You only need to look at an example and then you will be able to create your own.
Start by either typing in the keyboard shortcut to open the Linetype Manager, which is ‘lt’ enter. Or on the ribbon, go to the Home tab -> Properties panel -> Click the Linetype dropdown -> click Other.
As you can see at the top of the dialogue box, acadiso.lin is the file name that contains AutoCAD linetypes. Click on the File button at the top of the dialogue box.
By default you will see two .lin files in the AutoCAD Support directory.
I would suggest you create a copy of the acadiso.lin file. Select the file, right click and select copy. Then right click and select paste. The reason we create a copy is to not edit the original acadiso.lin file. (Something might go wrong and cause you serious trouble.) After copying the file, your dialogue will look like this. (Showing a third .lin file.)
Rightclick this new file and click Open. By default, you will open this text file and it should look like this.
If you look at the first linetype called Border, it consists of two rows. The first row is what the user sees when the linetype is selected in AutoCAD. The second row, starting with an ‘A’ is how AutoCAD draws the lines. A positive value is a line. A negative value is a gap and a 0 is a dot.
Now scroll down until you see the GAS line and select and copy two rows that are part of the GAS line. Scroll to the bottom area of the file and Paste the two rows as shown.
Now you can edit the copied GAS line to include something else, like Sewer lines eg SW. To do this you change the GAS text in the first line to SW.
Now change the second line to include SW.
Close the file, saving it.
Now select the new .lin to use to import linetype from and click Open.
In the Load linetype dialogue scroll down to the linetype named ‘SW’ select and click OK.
This has loaded the Linetype for you to use.
Now make the linetype current and draw a line.