diff --git a/pkg_resources/__init__.py b/pkg_resources/__init__.py
index c70b792e39..c10a88e5fd 100644
--- a/pkg_resources/__init__.py
+++ b/pkg_resources/__init__.py
@@ -109,7 +109,7 @@
 )
 
 
-T = TypeVar("T")
+_T = TypeVar("_T")
 # Type aliases
 _NestedStr = Union[str, Iterable[Union[str, Iterable["_NestedStr"]]]]
 _InstallerType = Callable[["Requirement"], Optional["Distribution"]]
@@ -118,7 +118,12 @@
 _MetadataType = Optional["IResourceProvider"]
 # Any object works, but let's indicate we expect something like a module (optionally has __loader__ or __file__)
 _ModuleLike = Union[object, types.ModuleType]
-_AdapterType = Callable[..., Any]  # Incomplete
+_ProviderFactoryType = Callable[[_ModuleLike], "IResourceProvider"]
+_DistFinderType = Callable[[_T, str, bool], Iterable["Distribution"]]
+_NSHandlerType = Callable[[_T, str, str, types.ModuleType], Optional[str]]
+_AdapterT = TypeVar(
+    "_AdapterT", _DistFinderType[Any], _ProviderFactoryType, _NSHandlerType[Any]
+)
 
 
 # Use _typeshed.importlib.LoaderProtocol once available https://github.com/python/typeshed/pull/11890
@@ -142,7 +147,7 @@ class PEP440Warning(RuntimeWarning):
 _state_vars: Dict[str, str] = {}
 
 
-def _declare_state(vartype: str, varname: str, initial_value: T) -> T:
+def _declare_state(vartype: str, varname: str, initial_value: _T) -> _T:
     _state_vars[varname] = vartype
     return initial_value
 
@@ -377,7 +382,7 @@ class UnknownExtra(ResolutionError):
     """Distribution doesn't have an "extra feature" of the given name"""
 
 
-_provider_factories: Dict[Type[_ModuleLike], _AdapterType] = {}
+_provider_factories: Dict[Type[_ModuleLike], _ProviderFactoryType] = {}
 
 PY_MAJOR = '{}.{}'.format(*sys.version_info)
 EGG_DIST = 3
@@ -388,7 +393,7 @@ class UnknownExtra(ResolutionError):
 
 
 def register_loader_type(
-    loader_type: Type[_ModuleLike], provider_factory: _AdapterType
+    loader_type: Type[_ModuleLike], provider_factory: _ProviderFactoryType
 ):
     """Register `provider_factory` to make providers for `loader_type`
 
@@ -2097,12 +2102,12 @@ def __init__(self, importer: zipimport.zipimporter):
         self._setup_prefix()
 
 
-_distribution_finders: Dict[
-    type, Callable[[object, str, bool], Iterable["Distribution"]]
-] = _declare_state('dict', '_distribution_finders', {})
+_distribution_finders: Dict[type, _DistFinderType[Any]] = _declare_state(
+    'dict', '_distribution_finders', {}
+)
 
 
-def register_finder(importer_type: type, distribution_finder: _AdapterType):
+def register_finder(importer_type: Type[_T], distribution_finder: _DistFinderType[_T]):
     """Register `distribution_finder` to find distributions in sys.path items
 
     `importer_type` is the type or class of a PEP 302 "Importer" (sys.path item
@@ -2276,15 +2281,17 @@ def resolve_egg_link(path):
 
 register_finder(importlib.machinery.FileFinder, find_on_path)
 
-_namespace_handlers: Dict[
-    type, Callable[[object, str, str, types.ModuleType], Optional[str]]
-] = _declare_state('dict', '_namespace_handlers', {})
+_namespace_handlers: Dict[type, _NSHandlerType[Any]] = _declare_state(
+    'dict', '_namespace_handlers', {}
+)
 _namespace_packages: Dict[Optional[str], List[str]] = _declare_state(
     'dict', '_namespace_packages', {}
 )
 
 
-def register_namespace_handler(importer_type: type, namespace_handler: _AdapterType):
+def register_namespace_handler(
+    importer_type: Type[_T], namespace_handler: _NSHandlerType[_T]
+):
     """Register `namespace_handler` to declare namespace packages
 
     `importer_type` is the type or class of a PEP 302 "Importer" (sys.path item
@@ -2429,9 +2436,9 @@ def fixup_namespace_packages(path_item: str, parent: Optional[str] = None):
 
 
 def file_ns_handler(
-    importer: Optional[importlib.abc.PathEntryFinder],
-    path_item,
-    packageName,
+    importer: object,
+    path_item: "StrPath",
+    packageName: str,
     module: types.ModuleType,
 ):
     """Compute an ns-package subpath for a filesystem or zipfile importer"""
@@ -2454,7 +2461,7 @@ def file_ns_handler(
 
 
 def null_ns_handler(
-    importer: Optional[importlib.abc.PathEntryFinder],
+    importer: object,
     path_item: Optional[str],
     packageName: Optional[str],
     module: Optional[_ModuleLike],
@@ -3321,7 +3328,7 @@ def _always_object(classes):
     return classes
 
 
-def _find_adapter(registry: Mapping[type, _AdapterType], ob: object):
+def _find_adapter(registry: Mapping[type, _AdapterT], ob: object) -> _AdapterT:
     """Return an adapter factory for `ob` from `registry`"""
     types = _always_object(inspect.getmro(getattr(ob, '__class__', type(ob))))
     for t in types: