The Complete Guide to Kashime (Japanese Rivets): Types, Sizing, and How to Set Them Cleanly

Mastering Kashime: The Essential Fastener for Leather and Fabric Crafts

Hello, everyone! It’s Yassy from Crafters! (・∀・)

If you enjoy leathercraft or making structured fabric bags, you have likely come across metal rivets. In Japan, these essential craft hardware pieces are known as kashime (カシメ). They are indispensable for joining pieces of leather securely or reinforcing heavy-duty bag handles.

However, stepping into a craft store or browsing an online supplier can quickly become overwhelming. You will see terms like single-cap (katamen), double-cap (ryomen), small (ko-gashime), large (o-gashime), short-post (tanjaku), and long-post (nagaji). It is easy to wonder: "Which one should I actually buy?"

If you choose the wrong kashime for your material thickness or project purpose, it might pop loose over time or bend sideways when hammered. On the flip side, once you understand the basic rules of selection and setting, kashime will become your go-to hardware for instantly elevating both the durability and the professional finish of your work!

In this guide for beginners, I will walk you through the basic structure of kashime, the differences between types, how to calculate the perfect post length, the essential tools you need, and expert tips for setting them flawlessly every time.

What Is Kashime? Basic Structure and Role in Crafting

A kashime (rivet) is a metal fastening piece used to clamp two or more layers of leather or fabric together. By applying pressure from above with a hammer and setter, the parts lock together permanently to create a reinforced bond.

They are widely used in stress points where stitching alone might fail under heavy load, or when joining thick leather pieces that are difficult to sew through by hand or machine. Beyond their practical strength, their metallic shine and vintage textures make them a popular decorative accent.

A Pair Made of Two Parts: "Atama" (Cap) and "Ashi" (Post)

A standard kashime set consists of two interlocking parts:

• Atama (Cap / Head): The rounded, umbrella-like top piece that sits visibly on the front of your material.
• Ashi (Post / Stem / Foot): The cylindrical base inserted from the backside of the material.

The mechanism is straightforward: you insert the post through a prepunched hole, place the cap over the protruding post on the other side, and strike it using a dedicated rivet setter (setting tool) and mallet. The top of the post flattens and flares outward inside the cap, locking the two pieces securely together.

Once properly set, a kashime cannot be disassembled without cutting or destroying the hardware with pliers. Choosing the right size and installing it accurately the first time is essential!

Choosing by Shape: Main Types of Kashime

Kashime rivets are generally divided into three categories based on their design: Single-Cap (Katamen), Double-Cap (Ryomen), and Decorative / Domed (Tama / Kazari).

1. Single-Cap Kashime (Katamen Kashime)

Single-cap kashime feature a smooth, rounded dome on the front cap, while the base of the post on the back has a hollow, indented center.

Key Features:

• Simple structure and relatively inexpensive.
• The back sits relatively flat, keeping bulk to a minimum.
• Ideal for hidden areas where the reverse side will not be seen.

Recommended Uses:Inside key cases, behind card pockets in wallets, interior bag pockets, or lining layers where the back of the rivet will be covered with fabric or leather.

2. Double-Cap Kashime (Ryomen Kashime)

Double-cap kashime feature identical rounded, finished caps on both the front and the back. Whether viewed from the face side or the reverse side, the appearance is polished and symmetrical.

Key Features:

• Provides a high-end, premium finish from any angle.
• Smooth outer edges that do not catch on clothing or scratch skin.
• Significantly boosts the overall quality and market value of your handmade items.

Recommended Uses:Bag handle attachments, shoulder strap joints, wristlets, key fobs, and the exterior of leather goods—any place where the reverse side will be visible or handled directly.

3. Domed and Decorative Kashime (Tama & Kazari Kashime)

Beyond standard rounded caps, there are high-domed ball-shaped rivets (tama-gashime) as well as decorative rivets featuring stamped patterns, star or heart shapes, or faux turquoise resin inlays.

Key Features:

• Adds three-dimensional depth and striking visual character.
• Matches specific aesthetic styles, such as rugged, vintage, Western, or bohemian designs.

Recommended Uses:Embellishments on leather jackets, accent points on keychains, or decorative bands on belts.

Quick Note: How Kashime Differs from Eyelets and SnapsKashime (Rivets): Completely seals the hole, permanently joining layers together.Hatome (Grommets / Eyelets): Leaves an open center reinforced with metal, designed for threading cords, rings, or laces.Hokku (Snap Fasteners / Spring Snaps): Functional hardware that can be snapped open and closed repeatedly.

Sizing Guide: How to Select the Right Cap Diameter and Post Length

The most common beginner mistakes happen during size selection. In Japanese craft terminology, kashime are measured by two parameters: Cap Diameter and Post Length.

1. Cap Diameter (Mini to Extra-Large)

The cap diameter determines both the visual presence and the holding surface area of the rivet. Here is a guide to standard Japanese sizing standards:

• Toku-sho (Extra Small / Mini, approx. 4.5mm – 5mm): Doll clothing, delicate jewelry, small coin purse details.
• Ko-gashime (Small, approx. 6mm): Key cases, card holders, lightweight small leather goods, fabric pouches.
• Chu-gashime (Medium, approx. 7mm – 9mm): Tote bag handles, shoulder straps, general leathercraft projects.
• O-gashime (Large, approx. 9mm – 12mm): Heavy tote reinforcement, belt attachments, tool pouches needing maximum strength.
• Toku-dai (Extra Large, 13mm and above): Heavy-duty workwear, rugged biker gear, or bold decorative statements.

If you are unsure where to start, Ko-gashime (6mm) is the standard for small goods, while Chu-gashime (around 9mm) is the sweet spot for bags and straps.

2. Post Length: The Golden Calculation Rule

Even more critical than the cap diameter is the post length. The same 6mm small kashime can come in short (tanjaku), standard (namiasi / chu-ashi), and long (nagaji) post variations.

If the post length is incorrect, you will never get a secure hold no matter how hard you hit it. Always use this golden formula:

The Golden Rule for Kashime Post Length:Total Material Thickness + 1.5mm to 3.0mm = Optimal Post Length

For example, if you are joining two pieces of 1.5mm thick leather together, your total thickness is 3.0mm.Adding 1.5mm to 3.0mm means you should look for a kashime with a post length of approximately 4.5mm to 6.0mm.

What Happens If the Post Is Too Long or Too Short?

• If the post is too long: When hammered, the stem will buckle and bend sideways inside the cap, causing the cap to sit crooked. It will also leave unwanted slack between your materials, making the rivet spin or wobble loose.
• If the post is too short: The tip of the post cannot reach far enough into the cap cavity to bite into place. It will not catch, and the cap will simply pop off immediately or under minimal stress.

Measure your stacked leather or fabric with a ruler or digital caliper before purchasing your hardware!

Plating Finishes and Base Metals

The finish (surface plating) dramatically influences the aesthetic tone of your finished project. Match your rivets to your other hardware pieces—such as swivel snaps, D-rings, and zippers—for a cohesive, professional appearance.

Popular Plating Finishes

• Nickel (Silver): Clean, modern, and versatile. Works great with contemporary leather designs and vibrant fabrics.
• Antique Gold (Kobi / Brass Patina): Muted and vintage with an aged patina. Pairs wonderfully with vegetable-tanned leather and rugged canvas.
• Gold (Polished / Pale Gold): Luxurious, bright, and elegant. Perfect for refined women’s accessories and statement bags.
• Black Nickel / Gunmetal: Cool, dark metallic tone. Excellent for masculine, modern, or tactical aesthetics.

Base Metals: Solid Brass vs. Iron

Even when two rivets have the identical antique gold finish on the surface, the core metal underneath can differ:

• Solid Brass (Shinchu): Naturally rust-resistant and possesses just the right malleability to deform smoothly and seat tightly when hammered. Brass is highly recommended for high-end leathercraft, items used outdoors, or goods meant to age beautifully over years of use.
• Iron / Steel (Tetsu): Inexpensive and widely available, but susceptible to moisture. Over time, rust can bleed through and stain adjacent leather or fabric. Best reserved for mockups, prototypes, or disposable craft novelties.

Essential Tools for Setting Kashime

To install kashime cleanly without damaging their appearance, use the right dedicated tools. Improvised alternatives almost always crush the hardware.

1. Hole Punch and Rubber Pound Board: A round drive punch matching the diameter of your rivet post (typically 2.0mm–2.5mm for small kashime, and around 3.0mm for large kashime). Always place a dense rubber pounding board beneath your material to protect your punch blade.
2. Dedicated Rivet Setter (Uchibo) and Anvil (Uchidai): This is the most crucial part! Never strike a kashime directly with a flat hammer face. You must use a concave rivet setter rod and a matching curved anvil (or round setter base) that fits the dome contour of the cap. Using flat metal will crush the rounded dome completely flat. Ensure your setter size strictly matches your kashime size (e.g., small setter for small kashime).
3. Wooden Mallet or Polyurethane / Rubber Hammer: Avoid standard metal hammers. A wooden mallet or poly mallet prevents mushrooming the back end of your setter rod and delivers a controlled, even impact.

Step-by-Step: How to Set Kashime Without Mistakes

Once your workspace is set up, follow these three simple steps for consistent, professional results:

Step 1: Punch a Clean, Accurate Hole

Mark your desired placement with an awl. Lay your stacked material flat on your rubber pounding board, hold your hole punch perpendicular (strictly at a 90-degree angle), and strike firmly with your mallet to pierce a clean hole through all layers.Tip: A hole that is too small will pinch and wrinkle the material around the post, while an oversized hole allows the rivet to shift off-center. Choose a punch that matches the post diameter or is slightly larger.

Step 2: Insert the Hardware and Rest on the Anvil

Push the post through the hole from the back of your project. Place the cap over the exposed post tip on the front side and press gently until you feel or hear a faint "click" as it temporarily catches.Next, align the bottom cap (or the bottom base) into the corresponding concave depression of your metal anvil base.

Step 3: Hold the Setter Straight and Strike in Controlled Taps

Place the concave tip of your rivet setter directly over the top cap. Ensure the setter rod is held completely vertical, not tilted in any direction.Using your mallet, tap straight down with moderate force. Do not attempt to smash it down in a single heavy blow! Instead, give it 3 to 4 steady, controlled taps, checking after each strike to see if the rivet has seated snugly against the material.

Troubleshooting Common Setting Mistakes

If your rivets aren’t setting properly, check these frequent causes and fixes:

Problem 1: The Rivet Bends Sideways or Collapses at an Angle

• Cause: The setter rod or mallet was angled upon impact, or the post is too long for the material thickness.
• Fix: Reduce your post length so it protrudes only 1.5mm–3mm past the material surface. Focus on holding your setter strictly perpendicular and striking dead-center from above.

Problem 2: The Rivet Spins or Remains Loose

• Cause: Insufficient striking force, a post that is too short to engage, or material that is too thin.
• Fix: Re-align your setter and deliver a slightly firmer blow. If the material is simply too thin, either switch to a "short-post" kashime or insert a discreet leather or reinforcement washer between layers to build up thickness.

Problem 3: The Cap Gets Scratched or Dented Flat

• Cause: Using a flat metal hammer face directly, or using a setter sized for a different diameter (e.g., using a medium setter on a small rivet).
• Fix: Always match the setter tool to the exact rivet cap diameter. You can also place a small scrap of thin leather or scrap fabric between the setter tip and the metal cap to cushion the strike and keep the plating mirror-smooth.

Yassy’s Project-by-Project Selection Ideas

Here are three practical examples from my own workshop to show how I choose kashime depending on the project:

Idea 1: Leather Keychains & Wristlet Straps

• Hardware Chosen: Double-Cap Small Kashime (or Medium), Solid Brass with Antique Gold finish.
• Why: Keychains are handled constantly from both sides, so a double-cap finish is essential to avoid rough edges. The antique gold develops a warm, vintage character that looks even better as the leather patinas with age.

Idea 2: Canvas Tote Bag Handle Anchors

• Hardware Chosen: Double-Cap Large Kashime, Nickel finish, Long Post.
• Why: Bag handles carry significant weight. Adding one or two large kashime right beside the stitch line dramatically increases tensile strength. Heavy canvas paired with thick leather handles creates significant stack height, making a long-post option mandatory.

Idea 3: Interior Pouch Lining Pockets

• Hardware Chosen: Single-Cap Small Kashime, Nickel finish, Short Post.
• Why: When securing an interior slip pocket to a lining fabric, the backside will be concealed between the lining and outer shell. A single-cap with a short post saves cost and prevents unnecessary bulk inside the seams.

Level Up Your Crafting with Kashime!

Working with metal hardware like kashime might seem intimidating at first, but the selection rules are actually very straightforward:

• Use Double-Cap when both sides are exposed, and Single-Cap when the back is concealed.
• Match the Cap Diameter (small, medium, large) to your project’s scale.
• Calculate the Post Length: Total thickness + 1.5mm to 3.0mm.
• Always use the correct concave setter and anvil, striking straight down.

Keep these fundamentals in mind, and you will be able to create sturdy, professional-looking leather and textile pieces with confidence. I encourage you to add kashime into your next project and explore the endless possibilities of handmade crafts!

If you found this guide helpful, please feel free to share it with your fellow crafters on social media. See you in the next article—happy crafting from Yassy!

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