For a heavy canvas tent which moves a fair bit in the wind? I’ve seen wooden ones which look like they’d split, and some Chinese-made 3 hole stainless ones (not going to risk a photo; link below) – can anyone recommend something better than the flimsy plastic ones I’ve got which keep going slack?

https://es.aliexpress.com/item/Multifunctional-Stainless-Steel-3-hole-Carabiner-Wire-Rope-Tightener-EDC-Tool-Fast-Tied-Rope-Cord-Fastener/32821819430.html

There’s no reason (decent) wooden ones would split. These look fine (depending on the thickness of the guyline)

https://www.amazon.co.uk/Wood-Tent-Sliders-Runners-Tensioners/dp/B017UOI6WW

A bit of slipping can be a good thing in bad weather.

A strain relief before tears happen.

Why not use either a Taut Line Hitch or a Midshipman’s Hitch? It’s what they are intended for. If you leave a long tail then they don’t work loose. Work on anything from 2mm dyneema line upwards. Worth knowing anyway in case you do have a breakage.

Yet another use for old toeclip straps ??

Hadn’t even thought of knots. Might be worth a shot.

Those wooden ones are a bit dear given I’d need two packets. Unless I DIYed them.

I was going to suggest DIY wooden ones to be honest. Good use for an old wooden curtain rail I reckon…

How many do you need? I reckon I have some nice ash that I can knock you up a few for postage and a pint as long as you don’t need them by the weekend. We use them on 180lb military tents and they have withstood 90mph winds better than most other tents on the camp.

Manton, thanks for the offer. I’d have to check but I think there are 30! I’m in Spain so the postage might be a bit expensive though.

No problem, but the offer is there. We regularly make them in the field with hand tools if they fall off and get lost, but never had one break.

For good quality plastic adjusters, look at Clamcleat line-lok. Not cheap but work well.

IMO, if your guy-lines are going slack, it’s more likely to do with the ropes than the sliders – is it that nasty super slippery nylon stuff?

You need some friction between the slider/rope to hold a heavy canvas tent (with movement) taught.  Most sliders have the facility to “lock” – which just introduces more friction once you’ve tightened them.  With the wooden ones you do this by crossing the rope over the slider and behind the knot – you would do this if it was going to be particularly windy.

Try just replacing one of the ropes with something with a bit of texture, see if that helps