It looks like a caricature of a green, pregnant space ship, but to sci-fi aficionados it is a coveted model of the Thunderbird 2 used in the filming of the mid-'60s British TV series of the same name.

"This is, like, the iconic thing," said Alan Stephenson of San Luis Obispo, a science-fiction fan who, as a modeler, specializes in James Bond film sets.

"It is a celebration of the things that you are a fan of, and of creating things that you could not go out and buy," Stephenson said, explaining the lure of modeling.

"There is something ingrained in us that likes playing with small things," said Steve Elliott, owner of HobbyTown USA in Petaluma, a sponsor of the annual hobby show held Saturday in Petaluma. "I love cars and being able to build a small-scale car is a way of having one that I can't afford."

More than 2,000 people attended the International Plastic Modelers Society hobby show at the Petaluma Community Center. It was the fourth and largest show that has been put on by the Santa Rosa chapter.

"It's getting bigger every year; it's nice to see," said Rob Sellards of Cloverdale, who demonstrated two model hydroplanes in the community center lake. "Every year, they open up another room and another club is there. I can see this continuing to get bigger."

The main draw was 350 plastic models entered in a competition. Most were airplanes and cars, many of a military design.

But the show also featured model trains, tiny steam-powered engines and boats that ranged from exacting models of Navy warships and Coast Guard vessels to sailboats and hydroplanes, all built to function.

New this year was a science-fiction room that had models of spacecraft from "Star Trek" and the movie "Independence Day," a full-size B9 robot and two R2D2s, one of which rolled out under its own power at the end of the day.

Steve Sansweet, a former Lucasfilm marketer and founder of a Petaluma museum dedicated to "Star Wars," had a variety of "Star Wars" masks and memorabilia.

"It was the right film for its time," Sansweet said. "We were coming off of Vietnam, Nixon, all this negative stuff, and here comes a film with good guys and villains and the good guys win."

In another room, David Palmer of Sonoma displayed his brightly polished, hand-tooled model steam engines, some that were small-scale recreations of actual engines. Among them was a copy of the first practical steam engine made by Sir Robert Alexander Watson-Watt in Scotland in 1892.

"It's the craftsmanship, the machining of the different metals and the fact that they work," said Palmer, whose interest stems from watching his grandfather build a steam engine in the 1940s.

There was a room dedicated to Legos, where thousands of the pieces were scattered across large tables.

"Legos will never go out of style," said Catina Haugen of Petaluma, who had her two sons at the show. "At our house, it is build, build, build."

Wedge-shaped fighting robots were another draw, as youngsters crowded around a Bash Bot table for two-minute matches.

"It is nice to build something to destroy other things," said Dan Chatterton of Petaluma, a Bot Bash enthusiast.

Eight-year-old Delaney Ortiz of Petaluma, who also has radio-controlled cars, boats and helicopters, won her match.

"You put it under the other bot, get to the edge and keep bumping it," she said of her strategy.

(You can reach Staff Writer Bob Norberg at 521-5206 or bob.norberg@pressdemocrat.com.)