I'm like the fiddler on the roof guy, I'm sticking with Tradition! We became a superpower without having to change these things so there's that.

60p and bigger are spikes / d is also used as an abbreviation for pence in UK don't ask me why I a Yank

We still use nail gauge in England

While the world uses Metrics, America uses Freedom Units🇺🇸

Europeans are saddled with Metric and Centigrade because the professional politicians making the laws (poor little darlings) are incapable of comprehending inches, feet, yards and, miles. They are also challenged that Zero Fahrenheit is 32 degrees below the freezing of water.

A penny is actually 2 pence coin back in the old days of England before they went metric. In British colonies especially in the West Indies/ Caribbean that used dollars and cents as their currency, a penny was two cents. This took me a little while to get used to here in the US. lol

In the UK money used to be divided in Pounds, Shillings and Pence the symbols for those were LSD hence the D in Pennies.

I thought ten a penny nails was the going rate in the era when blacksmiths hammered out nails in the slot on anvils, perhaps around the same time that penny was a standard days wage for feudal laborers. There was a time when people used to burn their houses down to get their nails back when moving.

Penny, feel any better, this is news to me at 72!

Changing from imperial (or older) measurement systems to metric enables exciting new ways to increase profits through shrink-flation. Want to pay the same for a gallon of milk but only get 3 liters? You can be sure you won't get 4 liters (on average) for the same price (unless the artificially jack up the gallon price in anticipation of the change over). And if gas starts being sold as liters, you can bet it will be half the cost per liter than a gallon. What a benefit to the consumer with lower prices! But by equivalent volume you will actually be paying nearly double the price. Antiquated measurement systems that used to be approximations have long been standardized. IMO, there is no GOOD reason to change from one measurement system to another when they are all mathematically convertible to each other anyway.

When the first one cent piece was minted we were still using British pennies as legal tender. Americans called the new cent piece a penny out of habit.

But there is a real reason for keeping the traditional measurements. The people who USE the nails know what size a 10 d nail is. They don't have to think about it.

Why are the keys on a computer keyboard arranged the way they are? Yeah, it's "tradition." But generations of people learned how to type using that arrangement of keys. And changing the layout would mean they all had to be retrained. It's the same thing with nail sizes. People don't need to know how many millimeters long a nail is. If they've worked at carpentry for any length of time, they know what a 10 d nail looks like. No need to retrain them.

a 16d nail in 1420/600 years ago would have been worth two days labor in 1420.
1 shilling/20p = £32.15 = $40.63 vs the skilled median wages of 2024 in US = $244 two days labor (£193.05) Nails are worth about 6x less in 2024 than in 1420.

You know what else America is the only country that does it? Landing men on the Moon. You'd think another country would have done that by now but nope. Only crazy America ever has.

Try finding the difference between sheet metal and plate metal, or paper vs cardstock.

I don't believe you. You show 2 pennies and call it 1 inch but you say they represent 1/4". Go figure. The rest of you photo of pennies is likewise off.