Arby's, best known for roast beef, is rolling out its first meatball sandwich in its latest effort to make its meaty menu stand out.

For Arby's, bringing out a limited-time sandwich is a pretty common occurrence. The chain adds items to its menu every few weeks to lure new customers and entice existing patrons to try something different.

Adding the Italian meatball sandwich to the menu this month is in some ways a logical extension for the brand. But in other ways it is a risk, albeit a calculated one.

Arby's has cemented itself in the fast-food industry as a go-to place for meat lovers. In 2014, it began using a new tagline "We have the meats" in a Fallon campaign featuring spots voiced by Ving Rhames. It went so far as to record and air the 13-hour process of brisket being smoked online when it launched its Smokehouse brisket sandwich.

Many of the sandwiches added to the menu in recent years, such as brisket, gryos and sliders, brought new tastes to Arby's customers but fell under the same broad deli-style meat umbrella the chain already had down with sandwiches such as turkey or roast beef.

Early on, Arby's focus was clearly roast beef. A framed menu from the 1970s hangs near the entrance to Arby's Atlanta test kitchen. It includes six varieties of roast beef sandwiches (priced from $1.19 to $1.39), plus a club, ham 'n cheese and a turkey deluxe. Today, the sandwich board reads like a who's who of meat, with sandwiches including brisket, corned beef, ham, angus steak, turkey, chicken, bacon and, of course, roast beef.

Arby's has tested so many sandwiches over the past few years and has seen Italian food concepts come up in conversation so often that VP-Brand Executive Chef Neville Craw said his team "had a joke that we could do just a spinoff menu completely comprised of different Italian sandwiches. It seemed to always just be there at the top."

Arby's introduced a Loaded Italian sandwich as a limited-time offer last summer. The ham, salami and pepperoni sandwich was a hit. By August 2015, Arby's began thinking about adding a meatball sandwich to the menu, according to Jim Taylor, senior VP-product development and innovation. It is just now making its debut.

"That's an example of probably a faster project. Anywhere from a year to 18 months is a lot of times how long it takes to get something to market," Mr. Taylor said, adding that items can take a lot longer if they require any capital spending or if it is being tested as a permanent item on the menu.

The meatball sandwich will be featured until the end of August. Then, Arby's will look at sales and customer feedback to determine whether it will return.

"It has to show us evidence that there would be demand on an everyday basis that would be incremental to the things we have on our menu in order for it to be considered and tested as something that we might add," Mr. Taylor said.

In June, the company also began testing a trio of city-themed sandwiches -- a New York pastrami, Philly cheesesteak and Chicago Italian beef -- in a couple of different markets.

In all, Arby's said it tests more than 1,000 ideas every year, and has customers try about 100 of those before making its decisions on which to add in restaurants. The effort is paying off. Arby's U.S. same-store sales have risen for 22 consecutive quarters. In 2015, Arby's was the 20th largest restaurant chain in the country, with U.S. systemwide sales up 8.6% to $3.45 billion, according to Technomic. Its growth rate outpaced that of larger chains including McDonald's, Burger King, Wendy's and Sonic, according to Technomic data.

Under Mr. Taylor, who honed his brand skills at Procter & Gamble and Darden before joining Arby's in 2014, and Mr. Craw, who celebrates his 12th anniversary with Arby's in August, the chain spends months researching, testing and tweaking those items before they get a green light.

Mr. Taylor said a lot of what the team does is "try to find what's the most memorable, craveable, best experience you had with a food item, and then how can we get as close as possible to that."

It took a while to get the newest sandwich, which features meatballs, marinara sauce and smoked provolone cheese, just the way the company wanted it. Meatball supplier Fontanini Italian Meats worked on hitting Arby's specifications on the meatballs themselves. Ingredients include a blend of mostly beef and some pork, along with Parmesan cheese and herbs, but no soy. After hitting the right taste notes, even the sizing of the meatballs had to be just right.

Then, Arby's tried various ways to layer the meatballs, sauce and cheese on the bread. Mr. Craw said his team spent weeks in a couple of restaurants working out operational kinks to ensure the sandwich would have enough sauce yet not get too soggy, for example.

Most new sandwiches require some kind of training for restaurant staff, such as knowing the thickness of slices of meat or the order in which toppings should be arranged. The Italian meatball brings other challenges, such as finding the right angle at which to place the sandwich in the box so the four meatballs remain nestled inside the bread.

"This one was categorically different in every step of the way," said Mr. Craw. "Usually we'll build a sandwich and then cut it in half. This one, we cut the bread in half before putting on the meatballs so that the ingredients stay together and that when you cut it, it doesn't send sauce, cheese and meatball flying over the cutting board. It definitely was a different animal."

The chef also decided the meatballs should be heated out of the sauce rather than in it. "If you hold it in the hot sauce long enough, counterintuitively, it will actually make the meatball drier," Mr. Craw said, noting that hot sauce draws the moisture from the inside out.

As the meatball project was proceeding, Arby's decided the Loaded Italian's initial run was successful enough that it became part of the permanent menu earlier this year. Now, Arby's will feature both sandwiches in its latest marketing from Fallon.

Atlanta-based Arby's plans to sell the $4.99 meatball sandwich for a limited time starting July 25, with advertising set to begin on Aug. 1. If the sandwich sells well, there is a chance it also could become part of the core menu.

Sometimes, items get to bypass the limited-time process. After testing more than 100 different ideas for cookies, a salted caramel and Ghirardelli chocolate version and a triple chocolate version made the cut for test markets. Within months, Arby's dessert sales doubled, Mr. Taylor said.

The cookies went straight to the permanent menu in May.