I have checked all old coupons and price is $5.99 for Woodworking Scribe Metric/Inch Precision T-Ruler (in Banggood). Basically copy coupon, view price history or create e-mail price alert. You probably want to know what is the best price?
Woodworking Scribe Metric/Inch Precision T-Ruler Aluminum Pocket Marking Gauge Carpentry Cross Calibration Hole Scribing Ruler – Metric
Latest coupon code price check (UTC time):
Banggood ($5.99)
Banggood warehouse is located in China. There are no active coupons for this product, but the price is pretty low isn’t it? Is it a reasonable price for this item? Well, according to CouponsFromChina database this price is the best in history (2 records).
Link: Banggood product page
Price: $5.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Price history (for all/most countries) for Woodworking Scribe Metric/Inch Precision T-Ruler is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).