If you wear fine quality shirts as I do (Thresher and Glenny, Hawes & Curtis, T.M Lewin, Stephens Brothers, Dunhill) you will have small pockets on the collars to take collar stiffeners. Some shirts will have flimsy plastic stays in them which will bend and distort after a few hot washes. Metal stays come in a range of sizes from 2 - 3 inches and I have tried them all. With very few exceptions 2 inches is the perfect length of stay for 90% of quality shirts. Longer stays will protrude from the pocket on the collar and distort it's shape. Larger size stays only suit shirts with very long (60's style) shirts. If you want them, I have stays in the larger sizes but I wouldn't recommend them - mail me for details.
eBay
200Pcs Plastic Collar Stays Stiffeners Stay Bones Shirt Men's Clear Collar Stays L4ME
Aliexpress UK
12 Pcs Collar Stiffeners 6cm, 12 mm width ,Formal Men Shirt Bones Inserts Stays Plastic White. Free and Fast Delivery with royal mail 2nd class post. Check my Listings for other sizes and accessories.
eBay
[4Pair] Stainless Steel Collar Stiffeners with 8 Magnets, Magnetic Collar Stays Metal Shirt Collar
Aliexpress UK
Close fit is not easy to shift, composite strong glue, stronger viscosity, not easy to warp, not easy to fall off. Thickened material is stiff and shaped, PVC material, thickness of about 30 silk, does not increase the weight of the collar, so that the collar is naturally shaped.
eBay
[3Pair] Stainless Steel Collar Stiffeners with 6 Magnets, Magnetic Collar Stays Metal Shirt Collar
Aliexpress UK
10x No Curl Collar Polo Shirt Collar Stays Men Suit Collar Stickers Shirt Collar.
eBay
8Pcs Stainless Steel Collar Stiffeners with 10 Magnets, Magnetic Collar Stays Metal Shirt Collar
Aliexpress UK
The 5.5cm collar bones are perfect for keeping your collar stiff and in place.
eBay
Adjustable Shirt Collar Support T-Shirt Stand Collar Shaper Shirt Anti-roll Fixed Shaper Collar Stay
Aliexpress UK
Approx size 50mm x 10mm x 0.3mm. Keep your smart shirt collars pristine and sharp with these collar stays.
eBay
Shirts Collar Stays Sticker Anti-roll T-Shirt Stand Collar Shaper Adhesive Fixed Pads Invisible
Aliexpress UK
Premium Material: The 6 pieces of collar stiffeners are all made of high quality stainless steel. You can use the appropriate one to fit different shirts.
eBay
Anti Roll Collar Stays Sticker Adhesive Prevent Curl Polo Shirts Fixed Pad Stand Collar Shaper Avoid
Aliexpress UK
It does not easily shift or deform. Fir Most Shirts: Whether you wear simple denim shirts, polos, or dress shirts, you need thickened PVC collar stays to prevent your collar from curling and sagging.
eBay
Stainless Steel Collar Stay Stiffeners Bones For Bussiness Party Shirt Men's Gift Silver Collar
Aliexpress UK