There are three ways to find out which replacement refills are right for your pen:

If you can’t find any helpful information based on the make and model of the pen, take out the refill and inspect it for any identifying marks. Many refills will have their own make and model numbers printed or embossed on the barrel. If you find a model number on your pen’s refill, try doing a web search for that model number and see what you find.

A word of caution, though: Manufacturers can use very similar model numbers for very different refills. Just because a refill pops up when you do a web search for the model number doesn’t necessarily mean it’s the one you need. Take a close look at any pictures and specifications for the new refill and see if they match the refill you need to replace.

For all the countless refill brands and models out there, many fall into a small number of standard styles. If you can’t find the exact same refill that your pen came with, you may be able to find a different refill of the same style that fits in your pen just as well.

This is the hardest and least reliable way to find the right refill for your pen. Many refills look similar at first glance but are different in subtle ways that make them incompatible. Some refills can even be the same style but vary slightly between brands in ways that affect compatibility. But if the first two methods fail, this one can often save the day.

To help you find the right refill style for your pen, we’ve created the following quick-reference guide with pictures to help you identify your refill by its style.

Here is a list of standard refill styles that are used in many different pens by many different brands. If you’re not sure what kind of refill your pen needs, there’s a good chance it’s one of these.

The D1 refill is commonly used in slim multi pens and mini-size pocket pens. It is smooth and cylindrical, about 6.7 cm long and 2 mm in diameter, and almost always made entirely of metal.

D1 refills generally use ballpoint ink. There are a handful of D1 refills that use gel ink, but they run out very quickly since gel ink gets used up much faster than ballpoint ink. In fact, a gel ink D1 refill may run out after just 2-3 pages of regular writing.

D1 refills are almost all interchangeable, but there are some exceptions. Most notably, the D1 refills made by Zebra are a tiny fraction of a millimeter wider than the D1 refills made by most other brands. This doesn’t stop Zebra D1 refills from fitting in other brands’ pens, but it often stops other brands’ D1 refills from fitting in Zebra pens. (Advanced tip: You can usually get around this problem by wrapping a small sliver of tape around non-Zebra D1 refills, making them just wide enough to fit securely in Zebra pens.)

To learn more about D1 refills and find out which ones are our favorites, be sure to check out our guide here.

The Parker-style refill is one of the most popular refill styles in the world. It is large enough to hold a good amount of ink yet small enough to fit in modestly sized pens. It is about 9.8 cm long and has an easily recognizable shape, with a long thin tip, a wide barrel, and a plastic end piece embedded with ratchet-like grooves. Parker-style refills are usually made of metal, but they can also be made of plastic.

Parker-style refills mostly feature ballpoint ink, but there are gel ink options too.

This refill style is officially known as the G2 refill, but most people call it Parker-style due to its close association with Parker pens and to avoid confusion with the popular Pilot G2 refill, which is a completely different style.

Parker-style refills are almost always interchangeable. One issue we’ve run into on rare occasions is that some unusually broad (greater than 1.0 mm) refills have oversized tips that don’t quite fit through the openings of some pens.

There are tons of great Parker-style refills to choose from, but some of our favorites include the Uni SXR-600 Jetstream ballpoint refills and the Ohto Flash Dry gel ink refill. For something a bit more exotic, Fisher Space Pen “PR” refills come with an adapter that lets you use them in most pens that take Parker-style refills.

The Euro-style refill is commonly used for both rollerball and gel pens. It is also known by a variety of other names, including Standard Rollerball, RB, and Pilot G2-style. Whatever name it goes by, it is about 11.1 cm long and 6 mm in diameter, with a short thin tip and a long cylindrical barrel. The barrel may be made of metal, plastic, or a combination of both.

Interestingly, although it looks quite different at first glance, the standard Uni-ball Jetstream ballpoint refill is interchangeable with many Euro-style refills.

More so than other standard refill styles, Euro-style refills can vary in critical ways from one brand to another, and you can’t always count on ones from different brands to be interchangeable. When in doubt, refer to our lists of recommended refills and compatible pens to see which combinations we’ve confirmed to work.

One issue that affects compatibility between brands is the shape of the tip. Some Euro-style refills have tips that stay thin all the way until it meets the barrel, while others have tips that widen as they get closer to the barrel. If a pen is designed to use one of the refills with a tip that stays thin, it might not be able to hold a refill with a tip that widens near the barrel.

Another issue that can cause compatibility problems is length. Some refills, such as Pentel EnerGel and Uni-ball Signo refills, are about 1-2 mm longer than other Euro-style refills. This isn’t always enough to affect compatibility, but it often is. (Advanced tip: If necessary, you can try cutting the extra 1-2 mm off of the end of one of these refills to make it fit better in pens from other brands.)

Lastly, a few refills—mainly some Pilot refills like the FriXion and Juice Up—have tapered ends that can affect compatibility with some pens.

We don’t want to make any sweeping recommendations for Euro-style refills since they aren’t always interchangeable, but if you don’t know which ones your pen needs, the Ohto ceramic rollerball refills and Pilot G2 gel ink refills are good options to start with.

These refills aren’t technically a standardized style, but they are popular enough that we wanted to include them here. They have a short thin metal tip and a wide cylindrical metal barrel. And, very importantly, they come in two lengths: short (9.7 cm) and long (10.8 cm).

These refills are widely praised for their smooth, vibrant ink, but it is important to make sure you get one that is the right length for your pen. The key is in the model number. Both the long and short refills have a four-digit model number such as 8126, but the model numbers of the short refills start with a “P” (e.g. P8126). So if you need a 9.7 cm refill, get one with a P in the model number, and if you need a 10.8 cm refill, get one without a P in the model number.

We currently only carry the 9.7 cm short version, which can be found here.

We’ve covered the most common refill styles above, but a lot of brands use their own proprietary refill styles too. If your pen’s refill doesn’t match any of the ones listed above, it might match one of these. They are listed from shortest to longest.

The pint-sized LAMY M22 refill can be found in some mini pens, most notably the LAMY Pico. It is about 6 cm long with a thin tip that is about one-third of its overall length.

The M22 refill comes with a gray plastic cap included. In addition to keeping the ink fresh when the refill isn’t being used, this cap can be plugged into the back of the refill, making it compatible with pens that take LAMY M16 refills.

About 3 cm shorter than a regular Pilot G2 refill, the G2 Mini refill isn’t available for sale on its own, but you can find it in G2 Mini gel pens.

Alternatively, you can take a regular Pilot G2 refill and cut the end down to the right length. Before you do that, though, you’ll need to use up enough of the ink so that you aren’t cutting into the ink or the translucent gel that holds the ink in place. You’ll also need to save the plastic plug from the end of the refill and put it back into the end of the refill after you cut it.

The Pilot BRFN refill is essentially a Parker-style refill that has had the last 1.2 cm cut off of the end. It is used in a variety of Pilot pens including the S20 and Dr. Grip ballpoint pens.

BRFN refills come in two varieties: the BRFN-10, which is made of plastic, and the BRFN-30, which is made of metal. Apart from this difference in materials, though, they work the same and are completely interchangeable.

The Pilot FriXion Ball Slim refill is found in a variety of FriXion erasable gel pens and multi pens. At first glance, it appears similar to an 8.8 cm Japan Type refill, but at about 3.6 mm in diameter, the FriXion Ball Slim refill is too wide to fit in pens that use Japan Type refills.

The Fisher Space Pen PR refill has a distinctive all-metal design. It is very similar to the Zebra F-Refill, but the two are generally not interchangeable.

Fisher Space Pen PR refills come with a plastic adapter that you can slide to the end, making them compatible with most pens that use Parker-style refills.

The Zebra F-Refill has a long thin tip and a slightly thicker, relatively short barrel. It can be made of metal, plastic, or a combination of both. And unlike most refills, replacement F-Refills generally come with a replacement spring included.

F-Refills are used in some of Zebra’s most popular pens, including their stainless steel F-301, F-402, and F-701 ballpoint pens. A.G. Spalding & Bros also uses this refill style in many of their ballpoint pens.

The F-Refill looks very similar to the Fisher Space Pen PR refill, but the two are generally not interchangeable.

The LAMY M16 refill is used by most LAMY ballpoint pens, and it is easily recognizable by the distinctive black plastic collar near the base of the tip section. The M16 doesn’t work in any non-LAMY pens, but Monteverde makes an excellent alternative refill for use in LAMY pens, featuring their “Soft Roll” low-viscosity ballpoint ink in a rainbow of colors.

The LAMY M66 refill is used in the LAMY Swift and Tipo rollerball pens. It is one of two LAMY rollerball refills—the other being the longer M63 refill—so make sure to get the one that is right for your pen.

The M66 is similar to a Euro-style refill. It is too wide to fit in non-LAMY rollerball pens, but LAMY pens that take the M66 can often take some Euro-style refills, too.

The standard Uni-ball Jetstream refill may look unique, but it meets all the essential measurements of a Euro-style refill and fits in many pens that take other Euro-style style refills from Uni-ball. As we mentioned in the above section on Euro-style refills, however, these refills aren’t always interchangeable, so be sure to refer to our lists of recommended refills and compatible pens to see which combinations we’ve confirmed work.

The LAMY M63 refill is used in the LAMY 2000, Aion, AL-Star, Safari, and Vista rollerball pens. It is one of two LAMY rollerball refills—the other being the shorter M66 refill—so make sure to get the one that is right for your pen.

The M63 is similar to a Euro-style refill but about 5 mm longer. It can’t fit in pens that take Euro-style refills, but Euro-style refills can sometimes fit in pens that take the M63 if you fill in the extra 5 mm gap behind the refill. One option is to take the spring out of an old pen and insert it behind the Euro-style refill. Another option is to create a spacer to put behind the Euro-style refill by cutting off a 5 mm long section from the back of an old refill.

The Parker rollerball refill has a distinctive tapering shape that looks kind of like a rocketship. It is 11.6 cm long and just over 7 mm in diameter at its widest point. As far as we’ve found, these refills will only work in Parker rollerball pens, and Parker rollerball pens will only work with these refills.

The standard Pilot Hi-Tec-C refill has long been a popular choice for machined metal pens, like the venerable CW&T Pen Type-A. Its distinctive characteristics are a long cylindrical plastic barrel and a disc-shaped collar between the barrel and the thin, needle-point tip.

The Hi-Tec-C refill is similar to but generally not interchangeable with the Uni-ball Signo UMR-1 refill.

The Uni-ball Signo UMR-1 is the refill companion to our hall-of-fame favorite Signo UM-151 gel pen, also known as the Signo DX. It looks a bit like the Pilot Hi-Tec-C refill, but instead of a disc-shaped collar and a thin needle-point tip, the UMR-1 has a cone-shaped collar that tapers down to a conical tip. (Or a needle-point tip in the case of the UMR-1ND.)

The UMR-1 is similar to other Signo UMR capped pen refills, including the UMR-5, UMR-7, UMR-8, and UMR-10 refills, but they are not fully interchangeable because the UMR-1 is about 1 cm shorter than the others. You can use a UMR-1 refill in a pen that uses any of those other UMR refills—you don’t even need a spacer to fill in the extra space behind the UMR-1—but you can’t use one of those other UMR refills in a pen that uses UMR-1 refills unless you cut off that extra 1 cm.

These refills go with many of Uni-ball’s capped gel pens, including the Signo Broad, Impact, Noble Metal, and Sparkling Glitter pens.

They are almost identical to the UMR-1 refill, except that their barrels are 1 cm longer. Pens that use these UMR-5/7/8/10 refills can also use UMR-1 refills without any need for a spacer to fill in the gap behind the UMR-1. Conversely, UMR-5/7/8/10 refills can’t fit in pens that use UMR-1 refills unless you cut off that extra 1 cm.