• Most strap-on harness kits have either a hole or an O-ring that you slot the dildo into, and usually come with at least one dildo to start you off. Once you discover the joys of strap-on sex though, you'll be hungry to try dildos in new shapes and sizes - or may be be ready to go bigger.

    This guide will give you all the information you need to choose the right dildo to fit your strap-on. And remember, with our generous returns policy you can always check your dildo in your harness at home and if it doesn't fit, just send it back.

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    Products featured:Red Rider G-Spot Strap On Harness Kit, Lovehoney Lifelike Realistic 6 Inch Dildo, Sportsheets O-Rings Set of 4

    How to Choose a Dildo That Fits Your Harness

    Whether you're looking for a shiny new dildo for your harness, or have a favourite dildo you want to use in a harness and aren't sure what size to go for, we can help.

    To choose a dildo that will fit in your harness, start by measuring the internal diameter of your O-ring. Make sure you're only measuring the space the dildo will go through, not the full width of the O-ring.

    To choose an O-ring or harness that will fit a favourite dildo you'd like to use in a strap-on, measure the circumference of your dildo at the part just above the flared base (where it will sit in the O-ring).


    Compatible Dildo Calculator

    Our handy calculator does the maths, so you don't have to!

    1. Are you looking for a new dildo?

      If the internal diameter of your O-ring is inches

      You will need a dildo with a circumference of: 3.90 inches (or slightly smaller)

      Browse our Harness Dildos category: all products are suitable to use in strap-on harnesses.

    2. Are you looking for a new harness to fit your dildo?

      If the circumference of your dildo is inches

      You will need an O-ring with a diameter of: 1.25 inches (or slightly larger)

      View our How to Choose a Strap-On Harness guide: all harnesses listed by O-ring diameter.


    Sportsheets Newcomers Strap-On Starter KitExample:Let's look at the Sportsheets Newcomers Strap-On Starter Kit.

    On the product page, under the 'How it measures up' section, you can see that it has an O-ring diameter of 1.25 inches.

    So, an example of a compatible dildo is the Tantus Charmer Silicone G-Spot Prostate Dildo.

    It has a circumference of 3.9 inches (a perfect match for our harness O-ring size) and it has a flared base meaning that we can just slip it through our O-ring.

    How to Put A Dildo In Your Harness

    Fetish Fantasy Beginner's Strap-On DildoTake our word for it, it's easiest to get your dildo in place before you put your harness on! If your harness has an interchangeable O-ring, make sure the O-ring is attached to the harness before you start.

    If your dildo is long and smooth with a flat, flared base like the Doc Johnson Platinum Silicone Slim Dildo, you can just slip it into the O-ring.

    If your dildo is large, has a big kink in it or has testicles like the Lovehoney Lifelike Realistic 6 Inch Dildo, you’ll need to approach it from the other end. Gently pinch the flared base and work it through the O-ring.

    Either way, a little water-based lubricant can help ease the dildo through the O-ring.

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    Need more help?

    You can Contact Customer Care, who will be able to help you find the perfect dildo for your harness. You can email, telephone or live chat to an experienced advisor 24 hours a day, 7 days a week.


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