Spencer Kieboom (Courtesy of Matt Stahley of Sportstar Designs via Hagerstown Suns)

The Rule 5 draft is among those annual offseason nuances that have the power to alter fortunes — or to have little impact on anything whatsoever. The basics are these: With an aim at preventing teams from hoarding major league-ready players in their minor league systems, any player who has served substantial time in the minors and is not on the 40-man roster by the deadline (this year, Friday) is vulnerable to selection by another team in a draft that takes place at the Winter Meetings in early December. If a team selects a player, he must slide onto that team’s 40-man roster right away, so only those teams with room participate in the draft.

In anticipation of Friday’s’s deadline, the Nationals added three prospects to their 40-man roster Thursday afternoon, infielder Chris Bostick, catcher Spencer Kieboom, and left-handed reliever Nick Lee. That trio, all of which impressed with big minor league seasons in 2015, is now safe from selection in the draft.

Because free agents are removed from the 40-man, the Nationals have ample space with which to work, and still have two more slots on the 40-man roster after the addition of Bostick, Kieboom and Lee. They can either use those slots to protect more players — such as former organizational Minor League Player of the Year Matt Skole or Bryce Harper’s left-handed throwing brother Bryan — or to select players from other teams in the draft.

The Nationals’ 40-man roster is loaded with the organization’s top prospects, some of whom would have been vulnerable to selection, some of whom — by dint of the fact that they signed more recently — would have been safe anyway. Pitchers who did not spend the majority of their seasons in the big leagues, such as Abel De Los Santos, A.J. Cole, Erik Davis, Matt Grace, Taylor Hill, Taylor Jordan, Rafael Martin and Sammy Solis, are all on the 40-man roster. The top catching prospect in the system, Pedro Severino, infielders Wilmer Difo and Trea Turner, and outfielder Brian Goodwin are also rostered.

The Nationals acquired Bostick, a former 44th round pick, from the Rangers prior to last season in the deal that sent Ross Detwiler to Texas. Bostick is in the midst of an impressive Arizona Fall League schedule, and is known for speed and character, more than blow-you-away tools. He reached Class AA Harrisburg this season, and led the Nationals minor league system with 31 stolen bases.

Kieboom is considered one of the top catchers in the Nationals system, and Baseball America rated him as the top defensive catcher in the Carolina League after he threw out 41 percent of those who attempted to steal against him. The Nationals drafted him out of Clemson in the fifth round of the 2012 draft, and have moved him methodically through the system. He reached Class A Potomac this season, where he caught Lucas Giolito, Reynaldo Lopez, and other top prospects as he became a Carolina League All-Star.

Lee jumped onto the radar with another strong season in which the lefty threw well enough at Class A Potomac to be promoted to Class AA Harrisburg by late June. Lee, who doesn’t fit the Nationals’ big-bodied pitcher’s mold but benefits from an unorthodox throwing motion, moved from starting to relieving before the 2014 season, and has struck out 271 batters in 249 innings since.