Cleveland
Cleveland C27639 Straight Flute Tap 1/4"-28 UNF Semi-Bottoming 4 Flutes HSS Black Oxide pneumatic accessory
Creates UNF threads in 1/4"-28 holes with a semi-bottoming, four-flute HSS design finished in black oxide
- TypeTaps
- H3 thread limit ensures precise 2B class fit
- High-speed steel construction resists wear during repeated tapping
- Black oxide finish reduces friction and prevents galling
- Semi-bottoming design threads close to blind-hole bottoms
- Straight flute geometry clears chips efficiently in through-holes
Thread cutting tap
The Cleveland C27639 is a straight flute tap designed for creating internal UNF threads in a 1/4"-28 size. It suits machinists and maintenance technicians who need to cut new threads or repair damaged ones in metal workpieces. The semi-bottoming design allows threading close to the bottom of a blind hole. Four flutes provide chip clearance during the cutting process.
High speed steel construction
The tap is manufactured from high speed steel with a black oxide surface treatment for wear resistance and reduced galling. A right-hand cutting orientation matches standard threading operations. The overall length measures 2 1/2 inches with a thread length of 5/8 inches. The H3 thread limit and 2B class of fit define the tolerance envelope for the finished thread.
UNF thread standard limits
This tool produces Unified National Fine threads to a 2B class of fit, which determines the allowable variation in pitch diameter and major diameter. The 75 percent thread drill size of 5.45 mm is specified for the tapping drill hole; using a different drill diameter will alter the thread height and engagement. The semi-bottoming chamfer limits the tap's ability to start threads at the very bottom of a blind hole. The straight flute geometry is not optimised for deep holes or high-speed production tapping.
Highlights
- H3 thread limit ensures precise 2B class fit
- High-speed steel construction resists wear during repeated tapping
- Black oxide finish reduces friction and prevents galling
- Semi-bottoming design threads close to blind-hole bottoms
- Straight flute geometry clears chips efficiently in through-holes
Specifications
| Brand | CLEVELAND |
|---|---|
| Type | Taps |
Questions about this item
What does the 1/4"-28 UNF thread specification mean for the holes this tap can cut?
It cuts unified national fine threads with a quarter-inch major diameter and 28 threads per inch, producing a class 2B fit when used with the recommended 5.45 mm drill size for 75 percent thread engagement.
What physical dimensions determine whether this tap fits my tool holder or workpiece?
The overall length is 2 1/2 inches with a 5/8 inch thread length, a straight-flute four-flute design and a semi-bottoming chamfer that requires clearance to the bottom of a blind hole.
How should I install and use this HSS black oxide tap to avoid the common mistake of breaking it in the hole?
Secure the tap in a suitable holder, align it perfectly perpendicular to the workpiece, use cutting fluid, and advance with steady pressure while frequently reversing to break chips — forcing it without chip clearance is the typical cause of breakage.
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