The 13.5mm springs are stronger than the 14.5mm springs. Note - These springs are suitable for traditional style letterboxes. If your letterbox uses this type of spring you should be able to see the spring behind the flap.
eBay
Outside Mailboxes Wall Mount Locking Letter Box Large Capacity Save Space Wide Opening Parcel Box for Outdoor Private House
Aliexpress UK
Wear eye protection when fitting springs. Arms 24mm long (can be shortened with wire cutters).
eBay
26 Letters English Piggy Bank Wooden Coin Money Saving Box Jar Coins Storage Box Desktop Ornament Home Decor Crafts Xmas Gift
Aliexpress UK
eBay
26 Letters English Piggy Bank Wooden Coin Money Saving Box Jar Coins Storage Box Desktop Ornament Home Decor Crafts Xmas Gift
Aliexpress UK
eBay
HOMCOM Weatherproof Wall Mounted Letter Box Post Box with Keys Anthracite Grey
Aliexpress UK
Removed from door ,so has been fitted before ,see pics for condition.
eBay
Wooden Coin Money Saving Box Jar Twenty-six Letter Piggy Bank Coins Storage Box Desktop Ornament Home Decor Crafts Xmas Gift
Aliexpress UK
Problem with a flapping letterbox?. Maybe your spring has broken. You could repair it with these. Made in the EU.
eBay
Letter Box Post Box Weatherproof Address Vintage Traditional Post Newspaper
Aliexpress UK
New spring and stainless steel hinge bar fitted. Supplied with new fixings, currently 62mm long which you can be trim to suit your door.
eBay
Mom Letter Shaped Empty Flower Gift Box Fashion Fillable Mom Flower Box for Celebrations DIY Present Decorations Mother Day
Aliexpress UK
2 to 3 Onion plants per plug. These plug plants, part of the 'Grow your own' range from Root Source. Growing instructions and how to care for your plants included. On behalf of the Root Source team.
eBay
Wooden Card Box Storage Organizer for Wedding Letter Holder Vintage Envelope Money Box Keepsake Event
Aliexpress UK