1. WHY I BOUGHT THEM

I have worn pinstripes for most of my years in the City. If you'd asked me why, I'd have given you two reasons without thinking.

They're slimming. Everybody knows that. The vertical line draws the eye up and down, and you look taller and narrower for it. At five foot four, I need every advantage I can get on the height side of things.

And they're professional. For as long as I can remember, men and women have both worn them to work, and in the City that mattered to me. A pinstripe said I worked there, exactly as it did for every man in the room.

Looking back, both reasons were really the same one. I was young, new to London and exactly where I wanted to be, and I wanted to look as though I'd always been there.

Are they slimming, though?

Apparently not. The science points the other way, and the effect has a name: the Helmholtz illusion, after the physicist Hermann von Helmholtz, who described it in 1867.

A square filled with horizontal lines looks taller and narrower than the same square filled with vertical ones. Helmholtz even noted that horizontal stripes on a dress could make the figure look taller.

In 2011, vision scientists at the University of York tested the idea, first on plain shapes and then on a drawing of a dress and pictures of a mannequin. They found that a horizontally striped shape had to be made 4.5 per cent wider before people judged it to be the same width as a vertically striped one. The effect held on the clothes too.

So the stripe I chose to look taller and slimmer was, on both counts, the wrong way round.

Are they professional, then?

The pinstripe came down from the top. Edward VII and George V both wore pinstripe trousers with their frock coats, and as the City grew in importance, the stripe became part of how a professional man looked.

Victorian Britain had a complicated relationship with money. You could have a great deal of it and still not count as a gentleman, because making money was connected with trade, and trade belonged to the lower classes.

So a banker had an interesting problem. His chief asset wasn't just his capital but his respectability, and he needed to look like someone you'd trust with your money without looking as though he was trying too hard.

The pinstripe managed that rather well. It looked professional because the professionals wore it, which is all professional ever means.

Women weren't allowed to become members of the London Stock Exchange until 1973, when fourteen were elected, Muriel Wood the first. By the time I arrived in the City, women wearing the same suits as the men was completely ordinary. It's wild to think that something that felt so ordinary to me had such a short history.

In 1975, American consultant John T. Molloy spelled out the uniform for Wall Street stockbrokers, a conservative three-piece pinstripe. Two years later he did the same for women, prescribing a navy skirted suit, a white shirt cut like a man's and a scarf tied like an ascot. It was close enough to an airline uniform that women flying to business meetings were sometimes asked for another bag of peanuts.

Fitting in has always been a bit of a guess. Fashion still hands out plenty of rules, but these days we mostly get to choose which ones to follow, rather than being issued a uniform by a man with a bestseller.

What I wear now

When I started my first job in the City, fresh from New Zealand, I had no idea what people wore there, so I did what everyone does somewhere new. I looked around, and I copied the room.

In those early days I bought a beautifully tailored pinstripe three-piece suit. I loved wearing it, and the first time I did, I felt like I belonged in this strange new City work club.

Now I think about it, it was exactly the three-piece Molloy had in mind for the stockbroker, and nothing like the skirted suit he would have wanted for me.

Waistcoats are coming back, so I'm on the lookout for a new suit to match that first one, just not for the same reasons.

I'm older now, and much less interested in fitting in or looking someone else's part. I don't want a new suit because pinstripes are slimming (since apparently they aren't), or because they say I work somewhere. I want one because I remember how I felt in that first suit. That memory is what keeps my love of the pinstripe alive.

I choose most things that way now, for the memory of a moment I hold dear. It's the same reason a hotel luggage sticker stayed on my snowboard for a decade. The things that carry those memories are my reminders of a life well lived.

2. OURS RUNS THE OTHER WAY

Somewhere along the way the pinstripe stopped being a signal of who belonged where. Women took a stripe built for men and made it theirs, and eventually it turned up on anyone, anywhere, on almost anything.

As two women building something together, we've done much the same. We took a line that used to tell people where they stood, and put it on the things we carry every day, in colour.

Ours run horizontally. Partly because Helmholtz says it's more flattering. Mostly because we'd rather you chose the things you carry the way I choose my suits now, for how they make you feel, even at work, rather than someone else's idea of what looks right.

3. IN THE STUDIO THIS WEEK

This week we've been grappling with something that's been with us since day one, which is how to show what a pocket is actually for. It does its work across a whole day, and social media gives you a single beat before someone scrolls on.

Right now, we're focusing on the office, partly because of this letter and partly because three friends of ours lost their reading glasses between the gym, a desk and a meeting room within a few months of each other and complained to us about that.

If you've seen our posts and still wondered what the pocket is for, reply and tell us. A real answer helps us more than you'd think.

If you've ever worn something because it made you feel like you belonged, I'd love to hear that story. And if someone comes to mind who still owns the suit from their first job, send this to them too.

Sera

These are the good days. Running the other way.